Update bazlets to latest

Looks like Bazlets never quite get updated. CI currently fails due to a
lack of /usr/bin/python which is addressed by using
ctx.which("python3"). The commit is:

[2d0cc7e] Migrate to python <David Ostrovsky>

Change-Id: Ie7e89c659d93a5e802f18a8f7506ed7c9d3ba763
diff --git a/WORKSPACE b/WORKSPACE
index b3e0d3f..1395239 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -12,7 +12,7 @@
 load("//tools:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "f30a992da9fc855dce819875afb59f9dd6f860cd",
+    commit = "e68cc7a45d9ee2b100024b9b12533b50a4598585",
     # local_path = "/home/<user>/projects/bazlets",
 )