Set custom delimiters for Vue

Normally, in Vue.js, you could use `{{ variable }}` to render the value
of some variable. In our setup however, Jinja expects to handle the
`{{}}` as a template. This change allows us to use `!{ variable }` to
render the value in our Vue templates.

js/index.js

@@ -35,5 +35,6 @@ const app = new Vue({
       const modal = modalOpen.getAttribute("data-modal");
       this.modals[modal] = true;
     }
-  }
+  },
+  delimiters: ['!{', '}']
 })