Fix plugin build with latest master snapshot api

Switch to the snapshot api for that matter, until a new release
containing the necessary api changes comes out.

Change-Id: I575a7be27a4968b5272c6bba153dee11158d17b5

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 0e5d75e..74f724c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -12,4 +12,4 @@
     "gerrit_api",
 )
 
-gerrit_api()
+gerrit_api(version = "3.3.0-SNAPSHOT")