docs(transition-state): update to gsap@3 (#2531)

see https://greensock.com/3-migration

Author: fratzinger

src/v2/guide/transitioning-state.md

@@ -18,7 +18,7 @@ All of these are either already stored as raw numbers or can be converted into n
 Watchers allow us to animate changes of any numerical property into another property. That may sound complicated in the abstract, so let's dive into an example using [GreenSock](https://greensock.com/):
 
 ``` html
-<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.20.3/TweenMax.min.js"></script>
+<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/3.2.4/gsap.min.js"></script>
 
 <div id="animated-number-demo">
   <input v-model.number="number" type="number" step="20">
@@ -40,14 +40,14 @@ new Vue({
   },
   watch: {
     number: function(newValue) {
-      TweenLite.to(this.$data, 0.5, { tweenedNumber: newValue });
+      gsap.to(this.$data, { duration: 0.5, tweenedNumber: newValue });
     }
   }
 })
 ```
 
 {% raw %}
-<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.20.3/TweenMax.min.js"></script>
+<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/3.2.4/gsap.min.js"></script>
 <div id="animated-number-demo" class="demo">
   <input v-model.number="number" type="number" step="20">
   <p>{{ animatedNumber }}</p>
@@ -66,7 +66,7 @@ new Vue({
   },
   watch: {
     number: function(newValue) {
-      TweenLite.to(this.$data, 0.5, { tweenedNumber: newValue });
+      gsap.to(this.$data, { duration: 0.5, tweenedNumber: newValue });
     }
   }
 })