We don't currently use SQLite for any production deploys, and testing every build against it is overkill.
I'm removing this to be a bit nicer to the Travis servers; if we start relying more on SQLite's performance
in the future we can always revert this commit.
The Travis config will now run tests on the following instances
* 5.3 + SQLite
* 5.3 + MySQL
* 5.3 + PostgreSQL
* 5.4 + MySQL
In other words, with the exception of Windows tech (MSSQL + Win server) this is a wide-coverage build config.
