Update bazlets to stable-2.15 revision to build with 2.15.4

Change-Id: I03b1e6d3e14d08faf080b24f2bbc3f2863612ca6
diff --git a/WORKSPACE b/WORKSPACE
index bbe2300..bf95d57 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "8faa61d19d53cc125ac7fd51eb213a496ab14f8d",
+    commit = "88570121c377a8a94c76915566114bf02113a7d9",
     #local_path = "/home/<user>/projects/bazlets",
 )