Wrap import in wizard check

assets/javascripts/wizard/initializers/custom-wizard-step.js.es6

@@ -1,10 +1,9 @@
-import CustomWizard from "../models/custom";
-
 export default {
   name: "custom-wizard-step",
   initialize(app) {
     if (window.location.pathname.indexOf("/w/") < 0) return;
     
+    const CustomWizard = requirejs("discourse/plugins/discourse-custom-wizard/wizard/models/custom").default;
     const StepModel = requirejs("wizard/models/step").default;
     const StepComponent = requirejs("wizard/components/wizard-step").default;
     const ajax = requirejs("wizard/lib/ajax").ajax;