Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I6de49e13972e052311b79b3c01e101b46f82c537

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index a4b6bc4..edfe9b5 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")