message: Update cython to 0.28.4
  This fix updates the cython to the latest versioned
  release of 0.28.4 (released in 07/07/2018).
diff: @@ -682,12 +682,12 @@ def tf_workspace(path_prefix="", tf_repo_name=""):
  tf_http_archive(
  name = "cython",
  - sha256 = "05e3eb7f06043f5ff2028338370329e71c29f57315e95f4dc6ad7c4971dd4c6f",
  + sha256 = "bccc9aa050ea02595b2440188813b936eaf345e85fb9692790cecfe095cf91aa",
  urls = [
  - "https://mirror.bazel.build/github.com/cython/cython/archive/0.28.3.tar.gz",
  - "https://github.com/cython/cython/archive/0.28.3.tar.gz",
  + "https://mirror.bazel.build/github.com/cython/cython/archive/0.28.4.tar.gz",
  + "https://github.com/cython/cython/archive/0.28.4.tar.gz",
  ],
  - strip_prefix = "cython-0.28.3",
  + strip_prefix = "cython-0.28.4",
  build_file = clean_dep("//third_party:cython.BUILD"),
  delete = ["BUILD.bazel"],
  )
  