docs(style-guide): close the button at 09-01

closes angular#1490

Author: Foxandxss

public/docs/_examples/style-guide/ts/09-01/app/heroes/shared/hero-button/hero-button.component.ts

@@ -4,7 +4,7 @@ import { Component, OnInit } from '@angular/core';
 // #docregion example
 @Component({
   selector: 'toh-hero-button',
-  template: `<button>OK<button>`
+  template: `<button>OK</button>`
 })
 export class HeroButtonComponent implements OnInit {
   ngOnInit() {