fix running mix tasks error

resources/js/bootstrap.js

@@ -1,6 +1,5 @@
 
 window._ = require('lodash');
-window.Popper = require('popper.js').default;
 
 /**
  * We'll load jQuery and the Bootstrap jQuery plugin which provides support
@@ -9,6 +8,7 @@ window.Popper = require('popper.js').default;
  */
 
 try {
+    window.Popper = require('popper.js').default;
     window.$ = window.jQuery = require('jquery');
 
     require('bootstrap');