Fix code indentation (vuejs#1428)

Author: nlitwin

src/v2/cookbook/form-validation.md

@@ -143,7 +143,7 @@ const app = new Vue({
     },
     validEmail:function(email) {
       var re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
-    return re.test(email);
+      return re.test(email);
     }
   }
 })