Upgrade bazlets to latest stable-2.15 to build with 2.15.17 API

Change-Id: I80baf9d76708fcc8e511b5fe9973ecf6b712dbf7

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 2148a88..8836e19 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "5f03aec7c72e743079ea2ecad5530f4684ca7d45",
+    commit = "ae1cd231b0262b2738e6c0593eb3c504209ad4f5",
     #local_path = "/home/<user>/projects/bazlets",
 )