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

Change-Id: Ieeade4fe5253bfde71612150d1e7fee5d6dbe8bd
diff --git a/WORKSPACE b/WORKSPACE
index 2cc9d57..5ade21d 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "587749a13fcd3c6970a5418ea4496febabb50cdb",
+    commit = "c15e64db2a87c0453427ff45f79d1ed3899b5d92",
     #local_path = "/home/<user>/projects/bazlets",
 )