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

Change-Id: I87aeb3154279c7a0b615191a2164810ee536c9e5
diff --git a/WORKSPACE b/WORKSPACE
index 12a9504..9c6ee9f 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "7ce9a3f58f030635b3a1229b7fb4c62ee7979bc8",
+    commit = "88570121c377a8a94c76915566114bf02113a7d9",
     # local_path = "/home/<user>/projects/bazlets",
 )