spec: fix sub-second precision errors on mysql

refs CNVS-7032

Change-Id: I3926ab0453be0181cae30a5698b32d096643bb32
Reviewed-on: https://gerrit.instructure.com/28615
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>