message: changed the download version of protobuf to 3.6.0
diff: @@ -34,7 +34,7 @@ NSYNC_URL="$(grep -o 'https://mirror.bazel.build/github.com/google/nsync/.*tar\.
  # 1.10 branch does not work. `make distclean` fails and blocks the build
  # process. For now we're hardcoding to the version which is used by
  # TensorFlow 1.9.
  -PROTOBUF_URL="https://mirror.bazel.build/github.com/google/protobuf/archive/396336eb961b75f03b25824fe86cf6490fb75e3a.tar.gz"
  +PROTOBUF_URL="https://mirror.bazel.build/github.com/google/protobuf/archive/v3.6.0.tar.gz"
  # TODO (yongtang): Replace the following with 'https://mirror.bazel.build/github.com/google/re2/.*tar\.gz' once
  # the archive has been propagated in mirror.bazel.build.
  RE2_URL="$(grep -o 'https://github.com/google/re2/.*tar\.gz' "${BZL_FILE_PATH}" | head -n1)"
  