Update bazlets to latest revision on stable-2.15

This updates the API to 2.15-rc2

Change-Id: Ie97dd838c19cd63df83cde3e7245caeeecd68495
diff --git a/WORKSPACE b/WORKSPACE
index 103178d..dd7acd0 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "9459f7606f3efe7c1b46703f9bee1a97ad623878",
+    commit = "28d12c28df242b21855d4bebf8cca12b9ffcb900",
 )
 
 #Snapshot Plugin API