message: Fix doc_target test which no longer works on stable/beta.
diff: @@ -584,6 +584,10 @@ fn doc_same_name() {
  #[cargo_test]
  fn doc_target() {
  + if !is_nightly() {
  + // no_core, lang_items requires nightly.
  + return;
  + }
  const TARGET: &str = "arm-unknown-linux-gnueabihf";
  let p = project()
  