list MariaDB as one of the supported engines

[anson1014]

Introduction

As bookshelf is largely dependent on Knex and since Knex very explicitly states support for MariaDB, update the list of supported engines to reflect that.

Motivation

This is to prevent the scenario where users view the existing list of supported engines and become demotivated from using bookshelf as they are afraid MariaDB will not be supported.

[ottok]

@ricardograca This has 10 +1's - could you please considering merging this?
Even though the project is not actively maintained, the software still works and this small docs update will surely not introduce any regressions, so it should be perfectly safe and easy to merge.

[robertsilen]

Hey @ricardograca , any chance of getting this merged, please?