Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I4073cc91cea303ad43d9f0aad50385f079eb7666
diff --git a/WORKSPACE b/WORKSPACE
index fe7c6f9..1ef2adc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -44,4 +44,4 @@
 gerrit_api()
 
 # Load snapshot Plugin API
-#gerrit_api(version = "3.0.xy-SNAPSHOT")
+#gerrit_api(version = "3.1.xy-SNAPSHOT")