Updating grpc to 1.13.1 for cpp

Change-Id: Ie85c4ee1446f26b123fe37a8e3d0a817dd5e637c
diff --git a/VERSION b/VERSION
index a551051..232f96f 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1,2 @@
-0.15.0
+0.15.1
+