Make full path to file visible when error occurs

This makes it easier to sort out where the error is coming from in issues like angular/di.js#63

That would be nice!
Hmm, when I reported angular/di.js#63, I was building with the latest gulp:

gulp --version
[16:47:06] CLI version 3.8.7
[16:47:06] Local version 3.8.7