fixing the millisecond time precision issue for mysql database>5.6.4

fixing the millisecond time precision issue for mysql database(>=5.6.4) by stripping the millisecond precision from time object.
The ActiveSupport::Time object for rails 4.2.1b is returning time object with millisecond precision,which is causing the delayed job to not be execute for mysql database.
 The detailed issue and my solution is mentioned in this [issue 95](https://github.com/collectiveidea/delayed_job_active_record/issues/95)