message: Re-simplify GitSource::query
diff: @@ -141,7 +141,7 @@ impl<'cfg> Source for GitSource<'cfg> {
  let src = self.path_source
  .as_mut()
  .expect("BUG: update() must be called before query()");
  - Source::query(src, dep, f)
  + src.query(dep, f)
  }
  fn update(&mut self) -> CargoResult<()> {
  