Upgrade bazlets to latest stable-3.1

To use the now mandatory https protocol for MAVEN_CENTRAL.

Bug: Issue 12170
Change-Id: I30e4f50c839cf9ee546bdcadd1fe5e7114240444

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index f097872..1f3201c 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "8c8df720486ebe0b60adccd0eceb1c8122edaf58",
+    commit = "968b97fa03a9d2afd760f2e8ede3d5643da390d2",
     #local_path = "/home/<user>/projects/bazlets",
 )