textahead: fix pango markup URL
The old one no longer works.
@@ -119,7 +119,7 @@ impl ObjectImpl for TextAhead {
.default_value(&*default.separator)
.mutable_playing()
.build(),
- // See https://developer.gimp.org/api/2.0/pango/PangoMarkupFormat.html for pango attributes
+ // See https://docs.gtk.org/Pango/pango_markup.html for pango attributes
glib::ParamSpecString::builder("current-attributes")
.nick("Current attributes")
.blurb("Pango span attributes to set on the text from the current buffer")
