message: Fix nightly test matching rustc "warning" output.
diff: @@ -37,15 +37,9 @@ fn exported_priv_warning() {
  p.cargo("build --message-format=short")
  .masquerade_as_nightly_cargo()
  - .with_stderr(
  + .with_stderr_contains(
  "\
  -[UPDATING] `[..]` index
  -[DOWNLOADING] crates ...
  -[DOWNLOADED] priv_dep v0.1.0 ([..])
  -[COMPILING] priv_dep v0.1.0
  -[COMPILING] foo v0.0.1 ([CWD])
  src/lib.rs:3:13: warning: type `priv_dep::FromPriv` from private dependency 'priv_dep' in public interface
  -[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
  "
  )
  .run()
  