set defaultLayout and partials render  questions in koa2  koa-views hbs  
1,How to set defautlayout with handlebars
2,my code:

``` javascript
app.use(views(__dirname+"/views", {
    extension: 'hbs',
    map: { hbs: 'handlebars' },
    options: {
        partials: {
            error: './error' 
        }
    }
}));
```

routes/index.js

``` javascript
var router = require('koa-router')();
router.get('/', async function (ctx, next) {
  ctx.state = {
    title: 'koa2 title'
  };

  await ctx.render('index', {
  });
})
module.exports = router;
```

views/index.hbs

``` html
{{> error }}

<h1>{{title}}</h1>
<p>Welcome to {{title}}</p>
```

first time render ok,
but, when i refresh the browser.display an error:

``` code
  xxx GET / 500 12ms -
{ Error: ENOENT: no such file or directory, open 'C:\study\koa2\koa2-hbs\views\error

<h1>{{message}}<\h1>
<h2>{{error.status}}<\h2>
<pre>{{error.stack}}<\pre>
.hbs'
    at Error (native)
  errno: -4058,
  code: 'ENOENT',
  syscall: 'open',
  path: 'C:\\study\\koa2\\koa2-hbs\\views\\error\n\n<h1>{{message}}<\\h1>\n<h2>{{error.status}}<\\h2>\n<pre>{{error.stack}}<\\pre>\n.hbs' }
```
