set pixels of drops after each update

picogora.p8

@@ -146,10 +146,14 @@ function update_drops()
   new_drops = {}
   for i=1,#drops do
     d = drops[i]
+    oldx = d.x
+    oldy = d.y
     update_drop(d)
     if d.y < 128 then
       add(new_drops, d)
     end
+    pset(oldx, oldy, bg)
+    pset(d.x, d.y, white)
   end
   drops = new_drops
 end