docs: use proper quotations instead of '*'

gtk/gtkwidgetpath.c

@@ -978,7 +978,7 @@ gtk_widget_path_iter_has_class (const GtkWidgetPath *path,
  * gtk_style_context_add_region().
  *
  * Region names must only contain lowercase letters
- * and '-', starting always with a lowercase letter.
+ * and “-”, starting always with a lowercase letter.
  *
  * Since: 3.0
  **/