message: extra targets -> targets in comments
diff: @@ -211,7 +211,7 @@ mod test {
  assert_eq!(metadata.default_target.unwrap(), "x86_64-unknown-linux-gnu".to_owned());
  - let targets = metadata.targets.expect("should have explicit extra target");
  + let targets = metadata.targets.expect("should have explicit target");
  assert_eq!(targets.len(), 2);
  assert_eq!(targets[0], "x86_64-apple-darwin");
  assert_eq!(targets[1], "x86_64-pc-windows-msvc");
  @@ -245,7 +245,7 @@ mod test {
  "#);
  assert!(metadata.targets.is_none());
  - // extra targets explicitly set to empty array
  + // targets explicitly set to empty array
  let metadata = Metadata::from_str(r#"
  [package.metadata.docs.rs]
  targets = []
  @@ -272,13 +272,13 @@ mod test {
  }
  }
  - // unchanged default_target, extra targets specified to be empty
  + // unchanged default_target, targets specified to be empty
  metadata.targets = Some(Vec::new());
  let (default, others) = metadata.targets();
  assert_eq!(default, HOST_TARGET);
  assert!(others.is_empty());
  - // unchanged default_target, extra targets non-empty
  + // unchanged default_target, targets non-empty
  metadata.targets = Some(vec!["i686-pc-windows-msvc".into(), "i686-apple-darwin".into()]);
  let (default, others) = metadata.targets();
  assert_eq!(default, "i686-pc-windows-msvc");
  