fix activesupport-suspend_callbacks for 4.1

activesupport 4.1 doesn't have CallbackChain inherit from Array anymore,
instead, it houses an internal array and delegates to it.

Change-Id: I5730f734be5e7c0422ac56245609043f52b6425a
test-plan: specs
Reviewed-on: https://gerrit.instructure.com/33081
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>
Product-Review: Jacob Fugal <jacob@instructure.com>
QA-Review: Jacob Fugal <jacob@instructure.com>