Merge branch 'stable-3.1' into stable-3.2

* stable-3.1:
  ContentTypeUtil: Add singleton scope
  Upgrade bazlets to latest stable-3.1 to build with 3.1.12 API
  Upgrade bazlets to latest stable-3.0 to build with 3.0.15 API
  Upgrade bazlets to latest stable-2.16 to build with 2.16.26 API
  Upgrade bazlets to latest stable-2.16 to build with 2.16.23 API

Change-Id: I64539e95e56258e182ff76e509cb8f7d22d5fd9d

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 4d3e0d3..872eb15 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "87fd5f0d0a89d01df13deaf2d21a4bdb3bc03cfd",
+    commit = "8dc0767541f16b35d2136eccebffd9ebe2b81133",
     #local_path = "/home/<user>/projects/bazlets",
 )