bundler 1.6 support

native bundler api for changing github sources to https

Change-Id: Ie6cc75b7279bf7bdb7bbb0e3f7423206ae5a05c7
Reviewed-on: https://gerrit.instructure.com/35834
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>