validate that routes are an array before merging with another Router instance

dist/router.js

@@ -70,6 +70,8 @@ export default class Router {
     }
     use(obj) {
         if (obj instanceof Router) {
+            if (!Array.isArray(obj.routes))
+                throw new TypeError("Routes must be an array.");
             this.routes = [...this.routes, ...obj.routes];
             this.sortRoutes();
         }