settings: include gtk+

since we use it's definitions

Reviewed-by: Bob Ham <bob.ham@puri.sm>

src/settings.h

@@ -8,6 +8,7 @@
 #define __PHOSH_SETTINGS_H__
 
 #include "menu.h"
+#include <gtk/gtk.h>
 
 #define PHOSH_TYPE_SETTINGS (phosh_settings_get_type())