Clean qt_sink code

include/spdlog/sinks/qt_sinks.h

@@ -35,7 +35,7 @@ public:
         // store the meta method object for later usage
         qt_object_ = qt_object;
         auto *metaobject = qt_object_->metaObject();
-        int methodIndex = metaobject->indexOfMethod(meta_method_name.c_str());
+        auto methodIndex = metaobject->indexOfMethod(meta_method_name.c_str());
         if (methodIndex == -1) {
             throw_spdlog_ex("qt_sink: qt_object does not have meta_method " + meta_method_name);
         }