Upgrade to a new Bazel version

This one has better performance and various new features. It also
prevents us from falling too far behind upstream.

Change-Id: I3b8e1c5bda886ea2e990523af9e6de2434c784be
diff --git a/third_party/protobuf/protobuf.bzl b/third_party/protobuf/protobuf.bzl
index d91cde4..cfcb69a 100644
--- a/third_party/protobuf/protobuf.bzl
+++ b/third_party/protobuf/protobuf.bzl
@@ -90,7 +90,7 @@
         "deps": attr.label_list(providers = ["proto"]),
         "includes": attr.string_list(),
         "protoc": attr.label(
-            cfg = HOST_CFG,
+            cfg = 'host',
             executable = True,
             single_file = True,
             mandatory = True,