spec: bump rspec

closer to 3.0, which we probably don't want to go to until
we can drop rspec 1 (rails 2)

Change-Id: I8affc4882bfc927a6d3b9bcc9c43fe5ab92cd3b7
Reviewed-on: https://gerrit.instructure.com/37326
Reviewed-by: Jon Jensen <jon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>