Fix #17967 - Fix related to regression on Windows.
Fix #17967 - Fix related to regression on Windows.

os.path.join(*self.dirs) produces an invalid path on windows.
ftp paths are always forward-slash seperated like this. /pub/dir.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator