message: Update astor version to fix which we are hitting in Python 3.7
diff: @@ -278,12 +278,12 @@ def tf_workspace(path_prefix = "", tf_repo_name = ""):
  tf_http_archive(
  name = "astor_archive",
  build_file = clean_dep("//third_party:astor.BUILD"),
  - sha256 = "ff6d2e2962d834acb125cc4dcc80c54a8c17c253f4cc9d9c43b5102a560bb75d",
  - strip_prefix = "astor-0.6.2",
  + sha256 = "95c30d87a6c2cf89aa628b87398466840f0ad8652f88eb173125a6df8533fb8d",
  + strip_prefix = "astor-0.7.1",
  system_build_file = clean_dep("//third_party/systemlibs:astor.BUILD"),
  urls = [
  - "https://mirror.bazel.build/pypi.python.org/packages/d8/be/c4276b3199ec3feee2a88bc64810fbea8f26d961e0a4cd9c68387a9f35de/astor-0.6.2.tar.gz",
  - "https://pypi.python.org/packages/d8/be/c4276b3199ec3feee2a88bc64810fbea8f26d961e0a4cd9c68387a9f35de/astor-0.6.2.tar.gz",
  + "https://mirror.bazel.build/pypi.python.org/packages/99/80/f9482277c919d28bebd85813c0a70117214149a96b08981b72b63240b84c/astor-0.7.1.tar.gz",
  + "https://files.pythonhosted.org/packages/99/80/f9482277c919d28bebd85813c0a70117214149a96b08981b72b63240b84c/astor-0.7.1.tar.gz",
  ],
  )
  