Upgrade bazlets to latest stable-2.15

- Bazel: Remove iteration over depset

Change-Id: Iffb4fda899eeb64847f244953d9bcb3b044cfe54

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 722df14..788ca64 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "a2830809bc277f55e094e8203fee04d9dc802e51",
+    commit = "4df6379dfb49746619dcf4764825916406365774",
     #local_path = "/home/<user>/projects/bazlets",
 )