Jshint remove fluff

JSHint gives a couple of empty lines and a line like "n errors" at the end. These last couple of lines are not useful to have in the location list, they show up this at the end of the location list:

||
|| 12 errors
||

So I filtered them out via errorformat. We now only get actual errors/warnings in the location list, which is consistent with the output we get from the other checkers.