Upgrade bazlets to latest stable-3.1 to build with 3.1.5 API

Change-Id: I9fc2b1dbed1f355ab64512e9790b129f5ea3da4f
diff --git a/WORKSPACE b/WORKSPACE
index 6318608..6dbae6f 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "cd715d269734e7bb0aa2fc4a01d2d2e279631cc7",
+    commit = "c6656e6a3ed76eb7e6d9a217cbe5d59c415efb9a",
     #local_path = "/home/<user>/projects/bazlets",
 )