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

Change-Id: I6e9efa22411ffc7d2fe4b55032270350410f0b84
diff --git a/WORKSPACE b/WORKSPACE
index 025c566..e853e4a 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "60296e8f7162f279e3885a92014bc69252935612",
+    commit = "88570121c377a8a94c76915566114bf02113a7d9",
     #    local_path = "/home/<user>/projects/bazlets",
 )