update lottie demo

Samples/UIWidgetsSamples_2019_4/Assets/Script/ImageTest.cs

                     child: new Column(
                         children: new List<Widget>
                         {
-                            AnimatedLottie.file("wine.json", frame: frame, curve: Curves.linear),
+                            new Lottie("wine.json", size: new Size(100, 100)),
                             new Container(
                                 width: 100,
                                 height: 100,

com.unity.uiwidgets/Runtime/widgets/LottiePainter.cs

         public int _round = 0;
         public float _frame = 0;
         public float _duration = 0;
+        public Size _size = null;
-        public Lottie(string path, float frame = 0, int round = -1) {
+        public Lottie(string path, float frame = 0, Size size = null, int round = -1) {
+            _size = size;
         }
 
         public override State createState() {
             }
             
             return new CustomPaint(
-                size: Size.infinite,
+                size: widget._size,
                 painter: new LottiePainter(
                     skottie: widget._skottie,
                     frame: _frame