Update bazlets to latest revision on stable-2.15

- Use bazel-cache instead of buck-cache

Change-Id: I2d800ea19f43128e43f5474f4b644f15b3a0da5d
diff --git a/WORKSPACE b/WORKSPACE
index 7eb9aae..be398a1 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "1419057b24e41cda9a6ee9d9c431b9005faf8190",
+    commit = "df6622a4e725b4d0bad99377f05749171a8c94b9",
     #    local_path = "/home/<user>/projects/bazlets",
 )