Fix: Missing annotation for appauthor argument
According to the appdirs doc string and code [1], the appauthor argument in all functions supports False as argument value to skip insertion of author directories.
[1] https://github.com/ActiveState/appdirs/blob/master/appdirs.py#L52
If you're reading about this commit from an autogenerated changelog entry, this should have no user-visible impact on how the stubs are interpreted by a type checker; it's just an internal change to how typeshed's tests work.
