require bundler 1.6, and rip out github https monkey patch

Change-Id: I57f23949cfd0e7b8032e5a3a6113e75eb416da31
Reviewed-on: https://gerrit.instructure.com/40820
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>