InputBar: mark constrictor as explicit

Suggested-By:

Clang-Tidy: Single-argument constructors must be marked explicit to
avoid unintentional implicit conversions

More info: https://clang.llvm.org/extra/clang-tidy/checks/google-explicit-constructor.html

src/timeline/InputBar.h

@@ -32,7 +32,7 @@ class InputBar : public QObject
     Q_PROPERTY(QString text READ text NOTIFY textChanged)
 
 public:
-    InputBar(TimelineModel *parent)
+    explicit InputBar(TimelineModel *parent)
       : QObject()
       , room(parent)
     {