Set default branch to voltha-2.13

Signed-off-by: Eric Ball <eball@linuxfoundation.org>
Change-Id: I6c956b50d6fab427fc4cbeb1a33371d1f6aac41d
diff --git a/.gitreview b/.gitreview
index 94a12ba..8e17557 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,3 +3,4 @@
 port=29418
 project=voltha-docs.git
 defaultremote=origin
+defaultbranch=voltha-2.13