Travis: Explicitly start mysql service during build.

Also move to test on PHP7.4 stable and WordPress 5.3

.travis.yml

@@ -1,7 +1,5 @@
 language: php
 
-sudo: false
-
 env:
   global:
     - WP_PHPUNIT=phpunit
@@ -26,11 +24,15 @@ matrix:
       env: WP_VERSION=4.4
     - php: 7.0
       env: WP_VERSION=4.9
+    - php: 7.4
+      env: WP_VERSION=5.3
     - php: 7.3
       env: WP_VERSION=5.2
     - php: 7.3
       env: WP_VERSION=5.0 WP_MULTISITE=1 COVERAGE=1 OUTDATED=1
     - php: 7.3
+      env: WP_VERSION=5.3 WP_MULTISITE=1 COVERAGE=1 OUTDATED=1
+    - php: 7.4
       env: WP_VERSION=master
     - php: hhvm
       env: WP_VERSION=4.7
@@ -65,7 +67,7 @@ before_script:
   - |
     # Install the specified version of PHPUnit depending on the PHP version:
     case "$TRAVIS_PHP_VERSION" in
-      7.3|7.2|7.1|hhvm|nightly)
+      7.4|7.3|7.2|7.1|hhvm|nightly)
         echo "Using bundled PHPUnit (7.*)"
         composer install --no-interaction --prefer-source
         export WP_PHPUNIT=vendor/bin/phpunit

composer.json

@@ -9,7 +9,7 @@
         }
     ],
     "require": {
-        "php": "^5.2|^7.0.0"
+        "php": "^7.1"
     },
     "require-dev": {
         "phpunit/phpunit": "^6.0",