spec: simple_cov vendored_gems report merging

Change-Id: I2421119792dcd6f8b02618c9ecfb050e00a104bd
Reviewed-on: https://gerrit.instructure.com/31013
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Tested-by: Shawn Meredith <shawn@instructure.com>