Update index.ejs (vuejs#865)

Author: cloudyan

themes/vue/layout/index.ejs

@@ -57,7 +57,7 @@
 </div>
 
 <div id="footer">
-  Released under the <a href="https://opensource.org/licenses/MIT" href="_blank">MIT License</a><br>
+  Released under the <a href="https://opensource.org/licenses/MIT" target="_blank">MIT License</a><br>
   Copyright &copy; 2014-<%- new Date().getFullYear() %> Evan You
 </div>