move bundler version check before ruby version check

really old bundler versions don't support the ruby directive,
so give an obtuse error

Change-Id: I7ef5cd3c48b628751f2c540ef42df3d557417f95
Reviewed-on: https://gerrit.instructure.com/37556
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>