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

Change-Id: I6d64684b41a45a02cb366978667e54332d24ee90

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index c684ab0..2dff5db 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",
 )