Upgrade bazlets to latest stable-3.1 to build with 3.1.3 API

Change-Id: I948a69038f4feb7c6ce4ce4921e886a0b28e8bb7

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 95ad98a..ec50441 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "968b97fa03a9d2afd760f2e8ede3d5643da390d2",
+    commit = "300de940c226c4ef7f0ce4baa90e278ae0fa840c",
     #local_path = "/home/<user>/projects/bazlets",
 )