message: fix typo in rustc.rs comment
diff: @@ -95,11 +95,11 @@ impl Rustc {
  }
  }
  -/// It is a well known that `rustc` is not the fastest compiler in the world.
  -/// What is less known is that even `rustc --version --verbose` takes about a
  -/// hundred milliseconds! Because we need compiler version info even for no-op
  -/// builds, we cache it here, based on compiler's mtime and rustup's current
  -/// toolchain.
  +/// It is a well known fact that `rustc` is not the fastest compiler in the
  +/// world. What is less known is that even `rustc --version --verbose` takes
  +/// about a hundred milliseconds! Because we need compiler version info even
  +/// for no-op builds, we cache it here, based on compiler's mtime and rustup's
  +/// current toolchain.
  ///
  /// https://github.com/rust-lang/cargo/issues/5315
  /// https://github.com/rust-lang/rust/issues/49761
  