fix shot axis

vacuum_gambit.p8

@@ -881,8 +881,8 @@ function gun_base:actually_shoot(x, y)
   --   shots from guns with
   --   widely varying angles)
   local m = munition.new{
-   dx=sin(a)*v,
-   dy=cos(a)*v
+   dx=cos(a)*v,
+   dy=sin(a)*v
   }
   m:spawn_at(x+xo, y)
  end