Update MariaDB connector to 1.1.7 - pick up bugfix

In rev 1.1.3, MariaDB fixed bug CONJ-34, which was throwing an error
when the DB connection was lost. This led to breakage in our code,
as the error was not being caught. CONJ-34 changed that so the
connector now throws an IOException, which is properly handled by
the ZEP code.