fix(chips): Fix adding new chips on demo page (#3426)

Author: dozingcat

src/demo-app/chips/chips-demo.ts

@@ -1,4 +1,4 @@
-import {Component, ElementRef} from '@angular/core';
+import {Component} from '@angular/core';
 
 export interface Person {
   name: string;
@@ -39,10 +39,10 @@ export class ChipsDemo {
     alert(message);
   }
 
-  add(input: ElementRef): void {
-    if (input.nativeElement.value && input.nativeElement.value.trim() != '') {
-      this.people.push({ name: input.nativeElement.value.trim() });
-      input.nativeElement.value = '';
+  add(input: HTMLInputElement): void {
+    if (input.value && input.value.trim() != '') {
+      this.people.push({ name: input.value.trim() });
+      input.value = '';
     }
   }