message: reverse erroroneous change of mutex type
diff: @@ -98,7 +98,7 @@ int main(int argc, char** argv)
  /* stay subscribed for a short interval */
  {
  - std::lock_guard<std::mutex> guard(session_closed_mutex);
  + std::unique_lock<std::mutex> guard(session_closed_mutex);
  session_closed_convar.wait_for(guard, std::chrono::seconds(30),
  [&](){ return session_has_closed; });
  }
  @@ -123,7 +123,7 @@ int main(int argc, char** argv)
  /* wait for session to be closed by peer */
  {
  - std::lock_guard<std::mutex> guard(session_closed_mutex);
  + std::unique_lock<std::mutex> guard(session_closed_mutex);
  session_closed_convar.wait(guard, [&](){ return session_has_closed; });
  }
  