Upgrade bazlets to latest stable-3.1 to build with 3.1.10 API

Change-Id: I7ac0009a088f054f60478a8d86b1394044168e63

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 6fbf259..55d335c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "3f9dadc615dc4053369a42d9ada37dafd8d4763c",
+    commit = "91ea277efd6d9f24c18d6ddeba65bed866b00872",
     #local_path = "/home/<user>/projects/bazlets",
 )