message: use universal initialization for lock construction
diff: @@ -78,7 +78,7 @@ std::shared_ptr<hal::Event> Executable::Run(const context::Context& ctx, std::si
  ((void (*)(void*, lang::GridSize*))entrypoint)(argvec, &index);
  }
  {
  - std::unique_lock<std::mutex> lock(mutex);
  + std::unique_lock<std::mutex> lock{mutex};
  if (++completed == threads) {
  cv.notify_all();
  }
  @@ -86,7 +86,7 @@ std::shared_ptr<hal::Event> Executable::Run(const context::Context& ctx, std::si
  });
  }
  {
  - std::unique_lock<std::mutex> lock(mutex);
  + std::unique_lock<std::mutex> lock{mutex};
  cv.wait(lock, [&]() { return threads <= completed; });
  }
  