Revert back to protobuf v3.0.0

Author: pcj

README.md

@@ -24,7 +24,7 @@ was limited exposed and documented proto generation capabilities in
 the main bazel repository.  This is a moving target.  The main goals
 of this project are to:
 
-1. Provide `protoc`, the protocol buffer compiler ([v3.1.0](https://github.com/google/protobuf/releases/tag/v3.1.0)).
+1. Provide `protoc`, the protocol buffer compiler ([v3.0.0](https://github.com/google/protobuf/releases/tag/v3.0.0)).
 
 2. Provide the language-specific plugins.
 

protobuf/internal/repositories.bzl

@@ -30,7 +30,7 @@ REPOSITORIES = {
         "kind": "git_repository",
         "name": "com_github_google_protobuf",
         "remote": "https://github.com/google/protobuf.git",
-        "tag": "v3.1.0",
+        "tag": "v3.0.0",
     },
 
     # This binds the cc_binary "protoc" into //external:protoc.  This