Strip '@' symbols when merging pull requests.

Currently all of the commits with 'X' in them cause person X to
receive e-mails every time someone makes a public fork of Spark.

marmbrus who requested this.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #1239 from pwendell/strip and squashes the following commits:

22e5a97 [Patrick Wendell] Strip '@' symbols when merging pull requests.