Documentation fix in download_blob_to_file

[lambainsaan]

The file object name is incorrect in the method documentation.

[busunkim96]

@lambainsaan Thanks for catching this!

[busunkim96]

Storage failure seems to be unrelated:

        if not 200 <= response.status_code < 300:
>           raise exceptions.from_http_response(response)
E           google.api_core.exceptions.TooManyRequests: 429 POST https://www.googleapis.com/storage/v1/b?project=precise-truck-742: The project exceeded the rate limit for creating and deleting buckets.