Fix Pausing after every Update

Updates would pause when any change has happened, not when no change has happened.

lib/src/Engine.dart

@@ -102,7 +102,7 @@ class Engine {
   /// If simulation should be advanced manually one time, prefer using step().
   void update() {
     // TODO: create hasUpdated/hasAdvanced method in simulation to abstract actual updating away
-    if (_grid.update().length != 0) running = false;
+    if (_grid.update().length == 0) running = false;
   }
 
   /// Advances Logic One Update