TMail was replaced by Mail in Rails 3

Change-Id: I7b0c1e31fc5f56464d4ca89fa23a1190b2541edb
Reviewed-on: https://gerrit.instructure.com/28730
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>