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/tools/build_rules/protobuf.bzl b/tools/build_rules/protobuf.bzl
index fe6af4f..d5f4284 100644
--- a/tools/build_rules/protobuf.bzl
+++ b/tools/build_rules/protobuf.bzl
@@ -19,8 +19,8 @@
     ],
   )
 
-def _do_proto_cc_library_outputs(attr):
-  basename = attr.src.name[:-len('.proto')]
+def _do_proto_cc_library_outputs(src):
+  basename = src.name[:-len('.proto')]
   return {
     'pb_h': '%s.pb.h' % basename,
     'pb_cc': '%s.pb.cc' % basename,
@@ -37,7 +37,7 @@
     '_protoc': attr.label(
       default = Label('//third_party/protobuf:protoc'),
       executable = True,
-      cfg = HOST_CFG,
+      cfg = 'host',
     ),
     '_well_known_protos': attr.label(
       default = Label('//third_party/protobuf:well_known_protos'),