Upgrade bazlets to latest stable-2.16

To use the now mandatory https protocol for MAVEN_CENTRAL.

Adapt rules_closure consumption.

Bug: Issue 12170
Change-Id: Id67dc2b88f22967130dd34217a2537ddf2c1e865

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 01bc31a..f467954 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "59529f046a5cb855d9fe3ee87110d53305ec69b9",
+    commit = "620a4eb3bc0749301043fd6a69570b61b86e742e",
     #local_path = "/home/<user>/projects/bazlets",
 )
 
@@ -16,9 +16,11 @@
 gerrit_polymer()
 
 # Load closure compiler with transitive dependencies
-load("@io_bazel_rules_closure//closure:defs.bzl", "closure_repositories")
+load("@io_bazel_rules_closure//closure:repositories.bzl", "rules_closure_dependencies", "rules_closure_toolchains")
 
-closure_repositories()
+rules_closure_dependencies()
+
+rules_closure_toolchains()
 
 # Load Gerrit npm_binary toolchain
 load("@com_googlesource_gerrit_bazlets//tools:js.bzl", "GERRIT", "npm_binary")