docs: fix engine.md

Note: Due to a mistake MariaDB support was listed as 10.1 and above, but that should be 10.3 and above.

ENGINE.md

 # Database Engine Support
 
-## v6-beta
-|  Engine |  Minimum supported version |
+## v6
+| Engine | Minimum supported version |
 | :------------: | :------------: |
-|  Postgre | [9.5 ](https://www.postgresql.org/docs/9.5/ ) |
-|  MySQL |  [5.7](https://dev.mysql.com/doc/refman/5.7/en/) |
-|  MariaDB |  [10.1](https://mariadb.com/kb/en/changes-improvements-in-mariadb-101/) |
-|  Microsoft SQL |  `12.0.2000` |
-|  SQLite |  [3.0](https://www.sqlite.org/version3.html) 
+| PostgreSQL | [9.5](https://www.postgresql.org/docs/9.5/ ) |
+| MySQL | [5.7](https://dev.mysql.com/doc/refman/5.7/en/) |
+| MariaDB | [10.3](https://mariadb.com/kb/en/changes-improvements-in-mariadb-103/) |
+| Microsoft SQL Server | `12.0.2000` |
+| SQLite | [3.0](https://www.sqlite.org/version3.html) |