Set Gerrit to 3.13.0-rc4

Change-Id: I75af73908051030a120dd0f539fb3a93e14a485b
diff --git a/Version.mk b/Version.mk
index 83c1862..4618651 100644
--- a/Version.mk
+++ b/Version.mk
@@ -1,4 +1,4 @@
 VERSION=3.13.0
-WAR_VERSION=3.13.0-rc3
+WAR_VERSION=3.13.0-rc4
 BRANCH=stable-3.13
-RELEASE=0rc3
+RELEASE=0rc4