Upgrade bazlets to latest stable-2.16 to build with 2.16.4 API

Change-Id: Ieb2c4c1b7083e43aeff486d0c3b5c23fb9814798
diff --git a/WORKSPACE b/WORKSPACE
index 9ebccc3..7c4d21f 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "09a18a88ebdada986d32c1f50581e8734a47939a",
+    commit = "c15e64db2a87c0453427ff45f79d1ed3899b5d92",
     #local_path = "/home/<user>/projects/bazlets",
 )