Upgrade bazlets to latest stable-2.15 to build with 2.15.15 API

Change-Id: I039087dfec361e875949ea2cf8a2b5fa67180dd4

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index c72b7e1..d89001f 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "d60efafe2fa2581d8b6f10aeb80beef5a77b8093",
+    commit = "d710dc4d8441475fbedae2171cf3cbafe6d80f23",
     #local_path = "/home/<user>/projects/bazlets",
 )