message: Update protobuf to 3.6.1.2
  protobuf 3.6.1.2 contains a fix for the Python3.7 compiler. This will help us
  create a nightly Python3.7 build for TensorFlow.
diff: @@ -347,11 +347,11 @@ def tf_workspace(path_prefix = "", tf_repo_name = ""):
  )
  PROTOBUF_URLS = [
  - "https://mirror.bazel.build/github.com/google/protobuf/archive/v3.6.1.1.tar.gz",
  - "https://github.com/google/protobuf/archive/v3.6.1.1.tar.gz",
  + "https://mirror.bazel.build/github.com/google/protobuf/archive/v3.6.1.2.tar.gz",
  + "https://github.com/google/protobuf/archive/v3.6.1.2.tar.gz",
  ]
  - PROTOBUF_SHA256 = "1ade182f91f0fa6c6116195def5d22270e01b9d03fe91319e4c6215022d0d24b"
  - PROTOBUF_STRIP_PREFIX = "protobuf-3.6.1.1"
  + PROTOBUF_SHA256 = "2244b0308846bb22b4ff0bcc675e99290ff9f1115553ae9671eba1030af31bc0"
  + PROTOBUF_STRIP_PREFIX = "protobuf-3.6.1.2"
  tf_http_archive(
  name = "protobuf_archive",
  