message: Fix a typo in an env var name
  Not actually used yet in rust-lang/rust, but may as well try to get it
  right on the first try.
diff: @@ -1650,7 +1650,7 @@ pub fn rustc_host() -> String {
  }
  pub fn is_nightly() -> bool {
  - env::var("CARGO_TEST_DIABLE_NIGHTLY").is_err()
  + env::var("CARGO_TEST_DISABLE_NIGHTLY").is_err()
  && RUSTC
  .with(|r| r.verbose_version.contains("-nightly") || r.verbose_version.contains("-dev"))
  }
  