Expose error code in Status.file by rcjsuen · Pull Request #1468 · nodegit/nodegit

Due to a structural mistake in descriptor.json, Status.file does not
expose git_status_file's error code in the rejected promise.

The fix is the correct the JSON and also add a test to ensure that
this case is covered should it happen again in the future.

Signed-off-by: Remy Suen <remy.suen@gmail.com>