Fix bazlets using latest stable-3.1 to build with 3.1.5 API

Change-Id: Icfd0555b054c29060f4b9aaf647b9e1b85ab7de9

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 57fb502..f7e0b8e 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "c6656e6a3ed76eb7e6d9a217cbe5d59c415efb9a",
+    commit = "51c1fd2758fcc1b900a80d4ebb037bc373f85d39",
     #local_path = "/home/<user>/projects/bazlets",
 )