message: fix(tests/cli/log_levels): Improve comparison error reporting
diff: #[macro_use]
  +extern crate difference;
  +#[macro_use]
  extern crate assert_cli;
  #[macro_use]
  extern crate lazy_static;
  @@ -48,12 +50,14 @@ pub fn log_levels() {
  env::set_current_dir(CWD.join("tests/fixtures/example")).unwrap();
  let output1 = assert_cli!(&BIN, &["build", "--trace"] => Success).unwrap();
  + let output1_stderr = str::from_utf8(&output1.stderr).to_owned().unwrap();
  assert_contains!(&output1.stderr, "[trace]");
  assert_contains!(&output1.stderr, "[debug]");
  assert_contains!(&output1.stderr, "[info]");
  let output2 = assert_cli!(&BIN, &["build", "-L", "trace"] => Success).unwrap();
  - assert_eq!(output1.stderr, output2.stderr);
  + let output2_stderr = str::from_utf8(&output2.stderr).to_owned().unwrap();
  + assert_diff!(&output1_stderr, &output2_stderr, " ", 0);
  let output = assert_cli!(&BIN, &["build", "-L", "debug"] => Success).unwrap();
  assert_contains_not!(&output.stderr, "[trace]");
  