fix(npmignore): only ignore the root /src but not nested ones

[afharo]

Running npm publish --dry-run...

before:

npm warn publish npm auto-corrected some errors in your package.json when publishing.  Please run "npm pkg fix" to address these errors.
npm warn publish errors corrected:
npm warn publish "repository" was changed from a string to an object
npm warn publish "repository.url" was normalized to "git+ssh://[email protected]/elastic/ebt.git"
npm notice
npm notice 📦  @elastic/[email protected]
npm notice Tarball Contents
npm notice 546B LICENSE.txt
npm notice 569B README.md
npm notice 1.0kB client/index.d.ts
npm notice 785B client/index.js
npm notice 872B index.d.ts
npm notice 431B index.js
npm notice 1.2kB package.json
npm notice 185B shippers/elastic_v3/browser/index.d.ts
npm notice 684B shippers/elastic_v3/browser/index.js
npm notice 315B shippers/elastic_v3/common/index.d.ts
npm notice 1.2kB shippers/elastic_v3/common/index.js
npm notice 183B shippers/elastic_v3/server/index.d.ts
npm notice 678B shippers/elastic_v3/server/index.js
npm notice 197B shippers/fullstory/index.d.ts
npm notice 669B shippers/fullstory/index.js
npm notice Tarball Details
npm notice name: @elastic/ebt
npm notice version: 1.1.0
npm notice filename: elastic-ebt-1.1.0.tgz
npm notice package size: 3.0 kB
npm notice unpacked size: 10.6 kB
npm notice shasum: 611d5928fa46110bdf77efc09c359f6938dc5c8c
npm notice integrity: sha512-AbM38xPdvHcpj[...]Ta23opw9KXtOg==
npm notice total files: 19
npm notice
npm notice Publishing to https://registry.npmjs.org/ with tag latest and default access (dry-run)
+ @elastic/[email protected]

after:

npm warn publish npm auto-corrected some errors in your package.json when publishing.  Please run "npm pkg fix" to address these errors.
npm warn publish errors corrected:
npm warn publish "repository" was changed from a string to an object
npm warn publish "repository.url" was normalized to "git+ssh://[email protected]/elastic/ebt.git"
npm notice
npm notice 📦  @elastic/[email protected]
npm notice Tarball Contents
npm notice 546B LICENSE.txt
npm notice 569B README.md
npm notice 1.0kB client/index.d.ts
npm notice 785B client/index.js
npm notice 529B client/src/analytics_client/__mocks__/logger.d.ts
npm notice 2.3kB client/src/analytics_client/__mocks__/logger.js
npm notice 2.5kB client/src/analytics_client/analytics_client.d.ts
npm notice 15.5kB client/src/analytics_client/analytics_client.js
npm notice 1.3kB client/src/analytics_client/context_service.d.ts
npm notice 4.1kB client/src/analytics_client/context_service.js
npm notice 281B client/src/analytics_client/index.d.ts
npm notice 659B client/src/analytics_client/index.js
npm notice 2.1kB client/src/analytics_client/logger_types.d.ts
npm notice 431B client/src/analytics_client/logger_types.js
npm notice 234B client/src/analytics_client/mocks.d.ts
npm notice 960B client/src/analytics_client/mocks.js
npm notice 698B client/src/analytics_client/opt_in_config.d.ts
npm notice 2.9kB client/src/analytics_client/opt_in_config.js
npm notice 1.6kB client/src/analytics_client/shippers_registry.d.ts
npm notice 2.8kB client/src/analytics_client/shippers_registry.js
npm notice 6.2kB client/src/analytics_client/types.d.ts
npm notice 431B client/src/analytics_client/types.js
npm notice 103B client/src/events/index.d.ts
npm notice 431B client/src/events/index.js
npm notice 3.1kB client/src/events/types.d.ts
npm notice 431B client/src/events/types.js
npm notice 113B client/src/mocks.d.ts
npm notice 842B client/src/mocks.js
npm notice 254B client/src/schema/index.d.ts
npm notice 431B client/src/schema/index.js
npm notice 4.5kB client/src/schema/types.d.ts
npm notice 431B client/src/schema/types.js
npm notice 743B client/src/schema/validation/excess.d.ts
npm notice 4.4kB client/src/schema/validation/excess.js
npm notice 102B client/src/schema/validation/index.d.ts
npm notice 861B client/src/schema/validation/index.js
npm notice 309B client/src/schema/validation/schema_to_io_ts.d.ts
npm notice 4.3kB client/src/schema/validation/schema_to_io_ts.js
npm notice 424B client/src/schema/validation/validate_schema.d.ts
npm notice 2.7kB client/src/schema/validation/validate_schema.js
npm notice 41B client/src/shippers/index.d.ts
npm notice 431B client/src/shippers/index.js
npm notice 670B client/src/shippers/mocks.d.ts
npm notice 1.1kB client/src/shippers/mocks.js
npm notice 1.1kB client/src/shippers/types.d.ts
npm notice 431B client/src/shippers/types.js
npm notice 872B index.d.ts
npm notice 431B index.js
npm notice 1.2kB package.json
npm notice 185B shippers/elastic_v3/browser/index.d.ts
npm notice 684B shippers/elastic_v3/browser/index.js
npm notice 2.3kB shippers/elastic_v3/browser/src/browser_shipper.d.ts
npm notice 8.9kB shippers/elastic_v3/browser/src/browser_shipper.js
npm notice 315B shippers/elastic_v3/common/index.d.ts
npm notice 1.2kB shippers/elastic_v3/common/index.js
npm notice 183B shippers/elastic_v3/common/src/__mocks__/build_url.d.ts
npm notice 758B shippers/elastic_v3/common/src/__mocks__/build_url.js
npm notice 343B shippers/elastic_v3/common/src/error_with_code.d.ts
npm notice 1.0kB shippers/elastic_v3/common/src/error_with_code.js
npm notice 230B shippers/elastic_v3/common/src/events_to_ndjson.d.ts
npm notice 727B shippers/elastic_v3/common/src/events_to_ndjson.js
npm notice 612B shippers/elastic_v3/common/src/report_telemetry_counters.d.ts
npm notice 2.2kB shippers/elastic_v3/common/src/report_telemetry_counters.js
npm notice 1.1kB shippers/elastic_v3/common/src/types.d.ts
npm notice 431B shippers/elastic_v3/common/src/types.js
npm notice 183B shippers/elastic_v3/server/index.d.ts
npm notice 678B shippers/elastic_v3/server/index.js
npm notice 3.8kB shippers/elastic_v3/server/src/server_shipper.d.ts
npm notice 16.3kB shippers/elastic_v3/server/src/server_shipper.js
npm notice 58B shippers/elastic_v3/server/src/server_shipper.test.mocks.d.ts
npm notice 685B shippers/elastic_v3/server/src/server_shipper.test.mocks.js
npm notice 197B shippers/fullstory/index.d.ts
npm notice 669B shippers/fullstory/index.js
npm notice 2.5kB shippers/fullstory/src/fullstory_shipper.d.ts
npm notice 11.9kB shippers/fullstory/src/fullstory_shipper.js
npm notice 111B shippers/fullstory/src/fullstory_shipper.test.mocks.d.ts
npm notice 1.2kB shippers/fullstory/src/fullstory_shipper.test.mocks.js
npm notice 166B shippers/fullstory/src/get_parsed_version.d.ts
npm notice 822B shippers/fullstory/src/get_parsed_version.js
npm notice 466B shippers/fullstory/src/get_properties_and_schema.d.ts
npm notice 4.3kB shippers/fullstory/src/get_properties_and_schema.js
npm notice 1.2kB shippers/fullstory/src/load_snippet.d.ts
npm notice 1.6kB shippers/fullstory/src/load_snippet.js
npm notice 11B shippers/fullstory/src/raw_snippet.d.ts
npm notice 3.4kB shippers/fullstory/src/raw_snippet.js
npm notice 655B shippers/fullstory/src/types.d.ts
npm notice 431B shippers/fullstory/src/types.js
npm notice Tarball Details
npm notice name: @elastic/ebt
npm notice version: 1.1.0
npm notice filename: elastic-ebt-1.1.0.tgz
npm notice package size: 35.8 kB
npm notice unpacked size: 152.5 kB
npm notice shasum: 14ce6395ac5b75acd5133cf4f7a2a1976602253c
npm notice integrity: sha512-yz1FyqUM7X0nL[...]va3c7ZDj0nTFQ==
npm notice total files: 91
npm notice
npm notice Publishing to https://registry.npmjs.org/ with tag latest and default access (dry-run)
+ @elastic/[email protected]