Implement mocha grep invert

[samcayford]

Allows the use of the mocha grep invert functionality in the LRS conformance test suite.

This adds the ability to exclude tests from a test run. I could not get a not-ed (^) grep regex to work in order to achieve this.

[samcayford]

Anyone?

[andyjohnson]

Hey Sam, thanks for the PR. This would make it into another round of updates to the Test Suite, but it likely won't version until we get a change that has conformance implications based on the xAPI Spec. Note that I'm not currently controlling this code/PRs, but I did want to reach out.

[samcayford]

Thanks for the info. Ideally we would like to clone the adlnet repo and have this functionality, so it would be nice to be in master even if no version is released, but i understand that might not be how your handle your repo. At least with this information we can worry less about conformance changes to your repo while we pull down my fork until it's merged (if i understand correctly)

Thanks