Added ifEE guard for EE specific parts of board milestone model

app/assets/javascripts/boards/models/milestone.js

+import { isEE } from '~/lib/utils/common_utils';
+
 export default class ListMilestone {
   constructor(obj) {
     this.id = obj.id;
     this.title = obj.title;
-    this.path = obj.path;
-    this.state = obj.state;
-    this.webUrl = obj.web_url || obj.webUrl;
-    this.description = obj.description;
+
+    if (isEE) {
+      this.path = obj.path;
+      this.state = obj.state;
+      this.webUrl = obj.web_url || obj.webUrl;
+      this.description = obj.description;
+    }
   }
 }