message: Update grpc to v1.12.1
  This fix updates grpc from to the newer versioned
  release of v1.12.1.
diff: @@ -428,11 +428,11 @@ def tf_workspace(path_prefix="", tf_repo_name=""):
  tf_http_archive(
  name = "grpc",
  urls = [
  - "https://mirror.bazel.build/github.com/grpc/grpc/archive/d184fa229d75d336aedea0041bd59cb93e7e267f.tar.gz",
  - "https://github.com/grpc/grpc/archive/d184fa229d75d336aedea0041bd59cb93e7e267f.tar.gz",
  + "https://mirror.bazel.build/github.com/grpc/grpc/archive/v1.12.1.tar.gz",
  + "https://github.com/grpc/grpc/archive/v1.12.1.tar.gz",
  ],
  - sha256 = "895b31310e718a61f7335759a778c068a6edde1c089883598a0830cbb7075673",
  - strip_prefix = "grpc-d184fa229d75d336aedea0041bd59cb93e7e267f",
  + sha256 = "f6afbfafa8e7b524727d1ff37ff22fe9c3dcca07bd864e7a9d1efabf1d15d13c",
  + strip_prefix = "grpc-1.12.1",
  )
  