message: tests: Fix dot test by not including whitespace.
  Rust 1.35 changed the behavior of the Debug trait to include the
  trailing comma in structs and other things. This deals with that
  by not including all of the whitespace.
  The Rust change that introduced this was
  Fixes
diff: @@ -1422,12 +1422,12 @@ fn dot() {
  let mut gr = Graph::new();
  let a = gr.add_node(Record { a: 1, b: r"abc\" });
  gr.add_edge(a, a, (1, 2));
  - let dot_output = format!("{:#?}", Dot::new(&gr));
  + let dot_output = format!("{:?}", Dot::new(&gr));
  assert_eq!(dot_output,
  // The single \ turns into four \\\\ because of Debug which turns it to \\ and then escaping each \ to \\.
  r#"digraph {
  - 0 [label="Record {\l a: 1,\l b: \"abc\\\\\"\l}\l"]
  - 0 -> 0 [label="(\l 1,\l 2\l)\l"]
  + 0 [label="Record { a: 1, b: \"abc\\\\\" }"]
  + 0 -> 0 [label="(1, 2)"]
  }
  "#);
  }
  