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

Change-Id: I37628377f500d98088d5a86837fd8ba2a0eaabcd

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 1a5a3af..c6153f6 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",
 )