small fix

include/c11log/details/blocking_queue.h

@@ -103,7 +103,7 @@ private:
     std::mutex mutex_;
     std::condition_variable item_pushed_cond_;
     std::condition_variable item_popped_cond_;
-    const std::chrono::hours one_hour (1);
+    static constexpr auto one_hour = std::chrono::hours(1);
 };
 
 }