message: Update cython to 0.28.3
  This fix updates the cython from (09/2017)
  to the latest versioned release of 0.28.3 (05/2018).
  The change was initally added in PR 20228 but was not applied
  for some reason. The fix updates again.
diff: @@ -682,12 +682,12 @@ def tf_workspace(path_prefix="", tf_repo_name=""):
  tf_http_archive(
  name = "cython",
  - sha256 = "6dcd30b5ceb887b2b965ee7ceb82ea3acb5f0642fe2206c7636b45acea4798e5",
  + sha256 = "05e3eb7f06043f5ff2028338370329e71c29f57315e95f4dc6ad7c4971dd4c6f",
  urls = [
  - "https://mirror.bazel.build/github.com/cython/cython/archive/3732784c45cfb040a5b0936951d196f83a12ea17.tar.gz",
  - "https://github.com/cython/cython/archive/3732784c45cfb040a5b0936951d196f83a12ea17.tar.gz",
  + "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",
  ],
  - strip_prefix = "cython-3732784c45cfb040a5b0936951d196f83a12ea17",
  + strip_prefix = "cython-0.28.3",
  build_file = clean_dep("//third_party:cython.BUILD"),
  delete = ["BUILD.bazel"],
  )
  