Upgrade bazlets to latest stable-2.15 to build with 2.15.9 API

Change-Id: I6a99858cbb068ebfb1e0b06bbd22e0d24bff22ba
diff --git a/WORKSPACE b/WORKSPACE
index f8767fd..645d66e 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "d4e586bd341207f0b8aafcbe7dbcd4843f852826",
+    commit = "ca34f0cf89b2e041ea7f4aa4b9696efc2d76746f",
     #local_path = "/home/<user>/projects/bazlets"
 )