Replace slots with Q_SLOTS

src/covermanager/coverfromurldialog.h

@@ -47,7 +47,7 @@ class CoverFromURLDialog : public QDialog {
   // Opens the dialog. This returns an image found at the URL chosen by user or null image if the dialog got rejected.
   AlbumCoverImageResult Exec();
 
- private slots:
+ private Q_SLOTS:
   void accept() override;
   void LoadCoverFromURLFinished();