fix(demo): pin vue @^2

Author: leeyeh

demo/leaderboard/index.html

@@ -58,7 +58,7 @@
     </div>
 
   </div>
-  <script src="//unpkg.com/vue/dist/vue.js"></script>
+  <script src="//unpkg.com/vue@^2/dist/vue.js"></script>
   <script src="//cdnjs.cloudflare.com/ajax/libs/tween.js/17.2.0/Tween.min.js"></script>
   <script src="../../dist/av-min.js"></script>
   <script src="./leaderboard.js"></script>

demo/live-query/index.html

@@ -162,7 +162,7 @@ <h1>LeanTodo</h1>
         data-canonical-src="https://s3.amazonaws.com/github/ribbons/forkme_right_white_ffffff.png"
     /></a>
     <script src="../../dist/av-live-query-min.js"></script>
-    <script src="https://unpkg.com/vue/dist/vue.js"></script>
+    <script src="//unpkg.com/vue@^2/dist/vue.js"></script>
     <script src="app.js"></script>
   </body>
 </html>

demo/settings/index.html

@@ -25,7 +25,7 @@
       </div>
     </form>
   </div>
-  <script src="//unpkg.com/vue/dist/vue.js"></script>
+  <script src="//unpkg.com/vue@^2/dist/vue.js"></script>
   <script>
 
 var LOCAL_STORAGE_KEY = 'js-sdk-demo/configs';