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

Change-Id: Ia0cb411566ab2ab002e217fecd61a0105a8e7ff5

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 7ea9a02..4b33be3 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",
 )