Middleware always defaults to html even if the path has a different extension.
I have configured koa-views with only the views' path which defaults the middleware to 'html'. But when I use ctx.render('index.ejs') the debugging tries to do this 'index.ejs.html' and gives me an undefined response.
To fix it I include the default option to ejs, which outputs index.ejs.ejs but renders normally.

I'm currently using koa@2, I don't know if this might be part of the problem.

Thanks in advance.

``` javascript
import convert from 'koa-convert';
import {wrap} from 'co';

import views from 'koa-views';

app.use(convert(views(VIEWS_PATH)));

app.use(async (ctx, next) => {
  ctx.render = wrap(ctx.render);
  await next();
});

app.use(async (ctx, next) => {
  await ctx.render('index.ejs', {message: 'Hello world!!!'});
  console.log(ctx.body);
});
```

``` json
"dependencies": {
    "co": "4.6.0",
    "ejs": "2.4.1",
    "koa": "2.0.0-alpha.3",
    "koa-convert": "1.2.0",
    "koa-views": "3.1.0"
  }
```
