Merge pull request #984 from m1gu3l:master

Do not rely on global L (pull request #984)
(Leaflet/Leaflet.markercluster#984)
according to [@m1gu3l](https://github.com/m1gu3l))
fix issue #874 (Does not work with ES6 imports for leaflet)

build/rollup-config.js

@@ -1,6 +1,7 @@
 
 // Config file for running Rollup in "normal" mode (non-watch)
 
+import inject from '@rollup/plugin-inject';
 import rollupGitVersion from 'rollup-plugin-git-version'
 import json from 'rollup-plugin-json'
 
@@ -36,8 +37,14 @@ export default {
 		legacy: true, // Needed to create files loadable by IE8
 		name: 'Leaflet.markercluster',
 		sourcemap: true,
+		globals: {
+			"leaflet": "L"
+		}
 	},
 	plugins: [
 		release ? json() : rollupGitVersion(),
+		inject({
+			L: "leaflet"
+		})
 	],
 };

package.json

@@ -4,6 +4,7 @@
 	"version": "1.4.1",
 	"description": "Provides Beautiful Animated Marker Clustering functionality for Leaflet",
 	"devDependencies": {
+		"@rollup/plugin-inject": "^4.0.1",
 		"git-rev-sync": "^2.0.0",
 		"happen": "^0.3.2",
 		"jake": "10.4.5",