(meta fix) Revert coffee-coverage v0.4.0 update.

I'm running into problems with versions of `coffee-coverage` greater than v0.2.0 (as described in benbria/coffee-coverage#19.) I'm reverting to a lower version, for now, to get coverage working again, until that gets figured out.

This reverts commit 7fcde2fb98a831201dad8414683053abf158fd26.
+ trying to fix coffee-coverage