Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I3be3ff0eeafd746800f11e231dade46149bd424b
diff --git a/WORKSPACE b/WORKSPACE
index aaaea58..94acf22 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -41,5 +41,5 @@
 # To build against a local api snapshot jar, simply add the `version` parameter
 # to the below `gerrit_api` macro, like:
 #
-# gerrit_api(version="3.0.10-SNAPSHOT")
+# gerrit_api(version="3.1.7-SNAPSHOT")
 gerrit_api()