Upgrade bazlets to latest stable-2.15 to build with 2.15.18 API

Change-Id: Id8241250344c7fb3bb7b8d2d28b3a4d582efde72

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 81eb163..e79a98f 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "d735ef54dfd38f99106d5635228156139c0b57fd",
+    commit = "ec949feac1b9dae6cc2c8c25d254f34924c54296",
     #local_path = "/home/<user>/projects/bazlets",
 )