Fix rabbits not moving

As a side effect, killer rabbits will attack, as E() encompasses both
movement and attacking. Not sure how to fix this... but moving+sometimes
attacking is better than never moving.

src/main/java/net/citizensnpcs/npc/entity/RabbitController.java

@@ -126,7 +126,7 @@ public class RabbitController extends MobEntityController {
 
         @Override
         public void E() {
-            if (npc == null) {
+            if (npc == null || !npc.isFlyable()) {
                 super.E();
             }
         }
@@ -203,4 +203,4 @@ public class RabbitController extends MobEntityController {
             return npc;
         }
     }
-}
+}