Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I663bc4b46c3f61842292a8fd4025f9f79be2b8b8

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index f784c84..95d75f0 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")