Merge branch 'change-mysql-version' of https://github.com/hackel/laradock into hackel-change-mysql-version

* 'change-mysql-version' of https://github.com/hackel/laradock:
  Add documentation on the MYSQL_VERSION variable.
  Allow specifying the version of MySQL to install in .env file.

docker-compose.yml

@@ -194,6 +194,8 @@ services:
     mysql:
       build:
         context: ./mysql
+        args:
+          - MYSQL_VERSION=${MYSQL_VERSION}
       environment:
         - MYSQL_DATABASE=${MYSQL_DATABASE}
         - MYSQL_USER=${MYSQL_USER}