Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I67a74986e8a87cb21ae7b5cd01cbfe17a400b408

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index dfa0c78..dc01a8c 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")