Make JSON_VALUE() RETURNING arg for mysql optional

fix: typo in README

Fix validatePlatform for MariaDB, check for instance of MariaDBPlatform

Versions of DBAL before 3.3 used or extended the MySQLPlatform when
connecting to MariaDB. Because of this the platform check was
requiring an instance of MySQLPlatform.

This commit fixes MariaDB compatibility with DBAL >=3.3, while remaining
 compatible with versions prior to that (for now).

Fixes #113

Allow flexibility in composer versions

Support ORM 3

Fix doctrine/lexer deprecations

Merge pull request #89 from SherinBloemendaal/master

Use PostgreSQLPlatform instead of PostgreSQL94Platform

Merge pull request #84 from willemverspyck/master

Add JsonArrayAgg and JsonObjectAgg

Merge pull request #83 from nyroDev/update_mariadb

Implement missing MariaDB and update doc to indicate MySQL is compatible

Merge pull request #76 from piotaixr/feature/dbal3.0

Make code compatible (and requiring) Doctrine ORM 2.10 and DBAL 3.0