Add entries for "Sam Brannen" to .mailmap

Author: sbrannen

.mailmap

@@ -26,5 +26,8 @@ Andy Clement <aclement@vmware.com>
 Andy Clement <aclement@vmware.com> <aclement@pivotal.io>
 Andy Clement <aclement@vmware.com> <aclement@gopivotal.com>
 Andy Clement <aclement@vmware.com> <andrew.clement@gmail.com>
+Sam Brannen <sbrannen@vmware.com>
+Sam Brannen <sbrannen@vmware.com> <sbrannen@pivotal.io>
+Sam Brannen <sbrannen@vmware.com> <sam@sambrannen.com>
 <dmitry.katsubo@gmail.com> <dmitry.katsubo@gmai.com>
 Nick Williams <nicholas@nicholaswilliams.net>