Correcting mailmap for shortlog

Change-Id: I83c239dc4a7ced77059261ae7c689d0ae6bd54cd
Reviewed-on: http://review.couchbase.org/30682
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>