`mix harness.check` still passes after a harness package has changed

[tonyvanriet]

If you update a harness package without changing the harness.exs, i.e. mix harness.update, a subsequent mix harness.check run will pass. Probably shouldn't since a change to the templates in the package would likely change the .harness output.

Currently harness.check uses a hash of the harness.exs to do its check. Seems like it would be reasonable to include the harness.lock file in that hash or do separate hashes and check both.

I came around looking for a quick way to include harness.lock in the hash. The current implementation of the hash and check seems very coupled to the manifest file only, so leaning towards adding a harness.lock hash check to the task.

Alternatively, we could just wipe out the .harness/.manifest.hash file when doing a harness.get or harness.update task.