Option to output names of differing files (e.g. only the --- .* \(original\)) lines of yapf -d

I might be missing this in the docs, but it would be great to have an option like
```
yapf -d --name-only
```
So if I use `yapf -d` as essentially a linter, I can get just the paths to the files with differences, rather than the entire diff. I can get the same effect by piping the output of `yapf -d` into grep or sed, but that adds some unnecessary-feeling postprocessing as well as not being totally safe, because it's possible for a line in the code diff itself to also match the "--- .* \(original\)" pattern.