message: revert protobuf version
diff: @@ -366,11 +366,11 @@ def tf_workspace(path_prefix = "", tf_repo_name = ""):
  )
  PROTOBUF_urls =[
  - "https://mirror.bazel.build/github.com/google/protobuf/archive/fe2eef4bf414ebb352cf11bcec633f1fd46ec876.tar.gz",
  - "https://github.com/google/protobuf/archive/fe2eef4bf414ebb352cf11bcec633f1fd46ec876.tar.gz",
  + "https://mirror.bazel.build/github.com/google/protobuf/archive/v3.6.0.tar.gz",
  + "https://github.com/google/protobuf/archive/v3.6.0.tar.gz",
  ]
  - PROTOBUF_sha256 = "b91b0ac9907af983877c960809dcad7a6dc8e4b06e34d32b7d66a12b9ea1fa17"
  - PROTOBUF_strip_prefix = "protobuf-fe2eef4bf414ebb352cf11bcec633f1fd46ec876"
  + PROTOBUF_sha256 = "50a5753995b3142627ac55cfd496cebc418a2e575ca0236e29033c67bd5665f4"
  + PROTOBUF_strip_prefix = "protobuf-3.6.0"
  tf_http_archive(
  name = "protobuf_archive",
  @@ -396,16 +396,6 @@ def tf_workspace(path_prefix = "", tf_repo_name = ""):
  strip_prefix = PROTOBUF_strip_prefix,
  )
  - tf_http_archive(
  - name = "bazel_skylib",
  - urls = [
  - "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/archive/2169ae1c374aab4a09aa90e65efe1a3aad4e279b.tar.gz",
  - "https://github.com/bazelbuild/bazel-skylib/archive/2169ae1c374aab4a09aa90e65efe1a3aad4e279b.tar.gz"
  - ],
  - sha256 = "bbccf674aa441c266df9894182d80de104cabd19be98be002f6d478aaa31574d",
  - strip_prefix = "bazel-skylib-2169ae1c374aab4a09aa90e65efe1a3aad4e279b",
  - )
  -
  tf_http_archive(
  name = "nsync",
  urls = [
  