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

Change-Id: Ia35b3d8b4f6450190d08ff2e3cb28782434a17bc

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 414d9e4..e40364d 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",
 )