Coverage compares last two commits, rather than master

[BlueRaja]

This plugin compares the last commit of a PR to the second-to-last commit, rather than to master.

This means if I decrease coverage from 50% to 45%, then increase it to 46%, the coverage passes (it should fail) But if I increase it from 50% to 55%, then decrease it to 54%, it fails (it should pass)