Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: Id3b3d410ec68e773993d8313ad1e7f37e1d7d848

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 6c1ab4b..82824b1 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")