resolve rails 3 logger.silence deprecation warnings

Change-Id: I06cdbd4bd8512e382e830a89a1efc246dae65889
Reviewed-on: https://gerrit.instructure.com/29040
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>