Update script tag to be inside body (umijs#464)

Author: nothingrealhappen

examples/purehtml/index.html

@@ -12,6 +12,6 @@
     Purehtml Example
   </div>
   <div id="purehtml-container" style="text-align:center"></div>
+  <script src="//localhost:7104/entry.js" entry></script>
 </body>
-<script src="//localhost:7104/entry.js" entry></script>
-</html>
+</html>