Drop support for MySQL 5.6

[schabdo]

MySQL 5.6 will reach EOL in 2021. Flyway 5.2.4 is the latest version still supporting MySQL 5.6. We won't be able to upgrade to a more recent version of Flyway until we discontinue support for MySQL 5.6 and move on to MySQL 5.7+.

Furthermore new version of Flyway will have better support for MariaDB by means forcing the JDBC driver to report MariaDB as a MySQL is not required anymore (cf. useMysqlMetadata in MariaDB connector parameters) in order to get it running:

org.flywaydb.core.api.FlywayException: Unsupported Database: MariaDB 10.5