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

Change-Id: I4554beaf9e769c0e1dabe767fde5debcdf099f8c
diff --git a/WORKSPACE b/WORKSPACE
index aee09c2..242b0d9 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "b0190b2d51f0987e0a021327bf4e0c34e4aa01f2",
+    commit = "c15e64db2a87c0453427ff45f79d1ed3899b5d92",
     #local_path = "/home/<user>/projects/bazlets",
 )