message: Clarifying the docs about test.only
  * Clarifying the docs about test.only
  It wasn't clear that test.only just applys to a single file.
  * Update GlobalAPI.md
diff: @@ -357,9 +357,9 @@ until the promise resolves as well.
  Also under the aliases: `it.only(name, fn, timeout)` or `fit(name, fn, timeout)`
  -When you are debugging a large codebase, you will often only want to run a
  +When you are debugging a large test file, you will often only want to run a
  subset of tests. You can use `.only` to specify which tests are the only ones
  -you want to run.
  +you want to run in that test file.
  Optionally, you can provide a `timeout` (in milliseconds) for specifying how
  long to wait before aborting. _Note: The default timeout is 5 seconds._
  @@ -376,7 +376,8 @@ test('it is not snowing', () => {
  });
  ```
  -Only the "it is raining" test will run, since it is run with `test.only`.
  +Only the "it is raining" test will run in that test file, since it is run with
  +`test.only`.
  Usually you wouldn't check code using `test.only` into source control - you
  would use it just for debugging, and remove it once you have fixed the broken
  