allow ruby 2.1.2 and bundler 1.6.3

Change-Id: I1ee8bf656f1ec78c1a2c754dc1fec857a2ab79bf
Reviewed-on: https://gerrit.instructure.com/36710
Reviewed-by: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>