message: Fix compiler warning on Visual Studio.
diff: @@ -50,7 +50,7 @@ namespace grpc_go_generator {
  grpc::string unexportName(grpc::string s) {
  if (s.empty())
  return s;
  - s[0] = std::tolower(s[0]);
  + s[0] = static_cast<char>(std::tolower(s[0]));
  return s;
  }
  @@ -58,7 +58,7 @@ grpc::string unexportName(grpc::string s) {
  grpc::string exportName(grpc::string s) {
  if (s.empty())
  return s;
  - s[0] = std::toupper(s[0]);
  + s[0] = static_cast<char>(std::toupper(s[0]));
  return s;
  }
  