Do not save MirrorFilter temporary vectors

core/src/mindustry/maps/filters/MirrorFilter.java

@@ -12,7 +12,7 @@ import mindustry.maps.filters.FilterOption.*;
 import mindustry.world.*;
 
 public class MirrorFilter extends GenerateFilter{
-    private final Vec2 v1 = new Vec2(), v2 = new Vec2(), v3 = new Vec2();
+    private static final Vec2 v1 = new Vec2(), v2 = new Vec2(), v3 = new Vec2();
 
     int angle = 45;
     boolean rotate = false;