Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I6c66eaab09b01558bf328e3ca913f416f76c1c4a

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 33f9091..6de4ac0 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -16,4 +16,4 @@
 gerrit_api()
 
 # Load snapshot Plugin API
-#gerrit_api(version = "3.0.xy-SNAPSHOT")
+#gerrit_api(version = "3.1.xy-SNAPSHOT")