invalidate the map display each time we repaint it

really we should only need to do this when the app-state changes

pkgs/maps/main.fnl

@@ -76,6 +76,7 @@ label.readout {
 ;; to fill the width of the screen plus a bit
 
 (fn cairo-the-map [self g]
+  (: (self:get_window) :invalidate_rect nil)
   (let [{ : lat : lon : zoom } app-state
         num-tiles-x (+ 0 (math.ceil (/ map-width tile-size)))
         num-tiles-y (+ 0 (math.ceil (/ map-height tile-size)))
@@ -116,7 +117,7 @@ label.readout {
 
 
 (fn osm-widget []
-  (Gtk.Label {
+  (Gtk.DrawingArea {
               :width map-width :height map-height
               :on_draw  cairo-the-map
               }))