Add explicit

src/queue/queue.h

@@ -38,7 +38,7 @@ class Queue : public QAbstractProxyModel {
   Q_OBJECT
 
  public:
-  Queue(Playlist *parent = nullptr);
+  explicit Queue(Playlist *parent = nullptr);
 
   static const char *kRowsMimetype;
 

src/queue/queueview.h

@@ -35,7 +35,7 @@ class QueueView : public QWidget {
   Q_OBJECT
 
  public:
-  QueueView(QWidget *parent = nullptr);
+  explicit QueueView(QWidget *parent = nullptr);
   ~QueueView();
 
   void SetPlaylistManager(PlaylistManager *manager);