Add MySQL configuration to turn off strict mode.

Default mode for MySQL 5.6.22 is 'STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION'
which raises an error if you try to insert a value into a column that can't
accomodate it:

  ActiveRecord::StatementInvalid: Mysql2::Error: Data too long for column

Previous versions would silently truncate this data and insert it anyway, which
is obviously pretty crap but is the easiest way to avoid these errors in this
case.