extends/include issue - koaNunjucks2 vs koa-views
In koaNunjacks2: - Works
`{% extends "master.njk %}`

In koa-views: - Nothing works
`{% extends "master.njk %}`
`{% extends "master %}`

Same everything, just replacing the view renderer.

Config: 
```
koa.use(koaNunjucks({
  ext: 'njk',
  path: __dirname+'/views',
  nunjucksConfig: {
    trimBlocks: true
  }
}));
```

```
var views = views(__dirname+'/views', {
	extension: 'njk',
	map: {
		njk: 'nunjucks'
	},
});
koa.use(views);
```
Traceback:
```
[4:42:16] Initialisation...
[4:42:16] NodeJS server started, it is running on port 3000

  Template render error: (unknown path)
    Error: template not found: root
      at Object.exports.prettifyError (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/lib.js:34:15)
      at /media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:489:31
      at eval (eval at _compile (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:568:24), <anonymous>:9:11)
      at createTemplate (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:213:25)
      at next (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/lib.js:210:13)
      at handle (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:253:25)
      at /media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:264:21
      at next (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/lib.js:207:13)
      at Object.exports.asyncIter (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/lib.js:214:5)
      at new_cls.getTemplate (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:243:17)
      at new_cls.root [as rootRenderFunc] (eval at _compile (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:568:24), <anonymous>:8:5)
      at new_cls.render (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:482:15)
      at new_cls.renderString (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/src/environment.js:328:21)
      at Object.module.exports.renderString (/media/DarkHawk/srv/NodesProjects/Vue/node_modules/nunjucks/index.js:80:14)
      at /media/DarkHawk/srv/NodesProjects/Vue/node_modules/consolidate/lib/consolidate.js:1174:11
      at /media/DarkHawk/srv/NodesProjects/Vue/node_modules/consolidate/lib/consolidate.js:144:5

```

I don't think it's relevant, but below that I'm using Socket.io.

I opened a [SO question](https://stackoverflow.com/questions/44795987/koa-views-nunjucks-error-template-not-found-master) first before realizing it was working with another package.

Maybe I misconfigured the thing. Yesterday it was working great when I tried Pug though :)


