Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: Id12643fe014fbb0e9ad9af9eecb7b629b181d7ea
diff --git a/WORKSPACE b/WORKSPACE
index c96568d..7d8e755 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -16,7 +16,7 @@
 gerrit_api()
 
 # Load snapshot Plugin API
-#gerrit_api(version = "3.0.xy-SNAPSHOT")
+#gerrit_api(version = "3.1.xy-SNAPSHOT")
 
 load("//:external_plugin_deps.bzl", "external_plugin_deps")