fix compilation error (#1609)

src/widgets/editors/markdowneditor.cpp

@@ -81,7 +81,7 @@ MarkdownEditor::MarkdownEditor(const MarkdownEditorConfig &p_config,
     connect(m_headingTimer, &QTimer::timeout,
             this, &MarkdownEditor::currentHeadingChanged);
     connect(m_textEdit, &vte::VTextEdit::cursorLineChanged,
-            m_headingTimer, QOverload<void>::of(&QTimer::start));
+            m_headingTimer, QOverload<>::of(&QTimer::start));
 }
 
 MarkdownEditor::~MarkdownEditor()

src/widgets/editors/markdowneditor.h

@@ -10,6 +10,7 @@
 
 class QMimeData;
 class QMenu;
+class QTimer;
 
 namespace vte
 {