Ignore all paths within .stversions folder

A POST request to scan a .stversions/test folder is not properly ignored.
See https://github.com/Zillode/syncthing-inotify/issues/10#issuecomment-60294270
Does this actually address the mentioned issue? `filepath.Base()` returns the last path component so if we're looking at `a/b/.stversions/foo` for whatever reason, `sn` ought to be `"foo"` here.