message: Fix signed-unsigned comparison warning in Driver.cpp
diff: @@ -491,7 +491,7 @@ static ::FILE *PrepareCommandsForSourcing(const char *commands_data,
  }
  ssize_t nrwr = write(fds[WRITE], commands_data, commands_size);
  - if (nrwr != commands_size) {
  + if (size_t(nrwr) != commands_size) {
  WithColor::error()
  << format(
  "write(%i, %p, %" PRIu64
  