message: Use an explicit UnGraphMap dependency
diff: //! # Example
  //!
  //! ```rust
  -//! use petgraph::prelude::*;
  +//! use petgraph::graphmap::UnGraphMap;
  //! use petgraph::algo::{dijkstra, min_spanning_tree};
  //! use petgraph::data::FromElements;
  //! use petgraph::dot::{Dot, Config};
  