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

Change-Id: I96568a456d991f9e847b8eaf87a0cc161f06d85e
diff --git a/WORKSPACE b/WORKSPACE
index 84d17fc..426492b 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "3995849fe742201d93e40f2b109dcff13dd0a4ed",
+    commit = "88570121c377a8a94c76915566114bf02113a7d9",
     #    local_path = "/home/<user>/projects/bazlets",
 )