Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I97ccb4b7a129454e83fa052e779bc3a174a29981

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index c6f29dc..da4190e 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")