Fixed fireball rollback mechanism.

frontend/assets/resources/prefabs/Fireball.prefab

@@ -24,11 +24,11 @@
     "_active": true,
     "_components": [
       {
-        "__id__": 6
+        "__id__": 7
       }
     ],
     "_prefab": {
-      "__id__": 7
+      "__id__": 8
     },
     "_opacity": 255,
     "_color": {
@@ -79,23 +79,20 @@
   },
   {
     "__type__": "cc.Node",
-    "_name": "Fireball1",
+    "_name": "animNode",
     "_objFlags": 0,
     "_parent": {
       "__id__": 1
     },
-    "_children": [],
-    "_active": false,
-    "_components": [
+    "_children": [
       {
         "__id__": 3
-      },
-      {
-        "__id__": 4
       }
     ],
+    "_active": true,
+    "_components": [],
     "_prefab": {
-      "__id__": 5
+      "__id__": 6
     },
     "_opacity": 255,
     "_color": {
@@ -145,20 +142,67 @@
     "_id": ""
   },
   {
-    "__type__": "cc.Animation",
-    "_name": "",
+    "__type__": "cc.Node",
+    "_name": "Fireball1",
     "_objFlags": 0,
-    "node": {
+    "_parent": {
       "__id__": 2
     },
-    "_enabled": true,
-    "_defaultClip": null,
-    "_clips": [
+    "_children": [],
+    "_active": true,
+    "_components": [
       {
-        "__uuid__": "ba12416b-eec3-4260-8402-7fc25b125624"
+        "__id__": 4
       }
     ],
-    "playOnLoad": false,
+    "_prefab": {
+      "__id__": 5
+    },
+    "_opacity": 255,
+    "_color": {
+      "__type__": "cc.Color",
+      "r": 255,
+      "g": 255,
+      "b": 255,
+      "a": 255
+    },
+    "_contentSize": {
+      "__type__": "cc.Size",
+      "width": 117,
+      "height": 55
+    },
+    "_anchorPoint": {
+      "__type__": "cc.Vec2",
+      "x": 0.5,
+      "y": 0.5
+    },
+    "_trs": {
+      "__type__": "TypedArray",
+      "ctor": "Float64Array",
+      "array": [
+        -32,
+        0,
+        0,
+        0,
+        0,
+        0,
+        1,
+        1,
+        1,
+        1
+      ]
+    },
+    "_eulerAngles": {
+      "__type__": "cc.Vec3",
+      "x": 0,
+      "y": 0,
+      "z": 0
+    },
+    "_skewX": 0,
+    "_skewY": 0,
+    "_is3DNode": false,
+    "_groupIndex": 0,
+    "groupIndex": 0,
     "_id": ""
   },
   {
@@ -166,13 +210,19 @@
     "_name": "",
     "_objFlags": 0,
     "node": {
-      "__id__": 2
+      "__id__": 3
     },
     "_enabled": true,
-    "_materials": [],
+    "_materials": [
+      {
+        "__uuid__": "eca5d2f2-8ef6-41c2-bbe6-f9c79d09c432"
+      }
+    ],
     "_srcBlendFactor": 770,
     "_dstBlendFactor": 771,
-    "_spriteFrame": null,
+    "_spriteFrame": {
+      "__uuid__": "e92702d5-d5fd-49e6-ab6b-2296b43fa6d6"
+    },
     "_type": 0,
     "_sizeMode": 1,
     "_fillType": 0,
@@ -197,7 +247,18 @@
     "asset": {
       "__uuid__": "d92d4831-cd65-4eb5-90bd-b77021aec35b"
     },
-    "fileId": "9ds3kDxvVFFqyr760jrV4a",
+    "fileId": "5f1s6pDt5F3rknJTu0gQW7",
+    "sync": false
+  },
+  {
+    "__type__": "cc.PrefabInfo",
+    "root": {
+      "__id__": 1
+    },
+    "asset": {
+      "__uuid__": "d92d4831-cd65-4eb5-90bd-b77021aec35b"
+    },
+    "fileId": "3824oBeVVL1KOAQ6Zd9CC5",
     "sync": false
   },
   {
@@ -208,6 +269,9 @@
       "__id__": 1
     },
     "_enabled": true,
+    "animNode": {
+      "__id__": 2
+    },
     "_id": ""
   },
   {