message: Fix doc for Bfs::next()
diff: @@ -247,7 +247,7 @@ impl<N, VM> Bfs<N, VM>
  }
  }
  - /// Return the next node in the dfs, or **None** if the traversal is done.
  + /// Return the next node in the bfs, or **None** if the traversal is done.
  pub fn next<G>(&mut self, graph: G) -> Option<N>
  where G: IntoNeighbors<NodeId=N>
  {
  