Update bazlets to latest stable-2.15 to build with 2.15.4 API

Change-Id: Id96e5e3914ef6b192d98ef9b04359a819f4a6b01
diff --git a/WORKSPACE b/WORKSPACE
index 56b31e9..6bed164 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "d7597f93ef70e3fdcb95684287816735344242ba",
+    commit = "88570121c377a8a94c76915566114bf02113a7d9",
     #    local_path = "/home/<user>/projects/bazlets",
 )