message: Use compact json for the tensor mapping
diff: @@ -1492,6 +1492,8 @@ std::string GetTensorMappingJson(const poplar::Graph& graph,
  root["mappings"] = mappings;
  Json::StreamWriterBuilder json_builder;
  + json_builder["indentation"] = "";
  + json_builder["commentStyle"] = "None";
  std::string json_msg = Json::writeString(json_builder, root);
  if (VLOG_IS_ON(2)) {
  