fix missed reference to std::filesystem

src/Configuration.cpp

@@ -238,7 +238,7 @@ void Configuration::refresh()
             message << "config file modified, reloading " << path;
             sb::Log::log(message, sb::Log::DEBUG);
             merge(path);
-            config_modification_time = std::filesystem::file_time_type::clock::now();
+            config_modification_time = fs::file_time_type::clock::now();
             sb::Delegate::post("reconfig");
         }
     }