one ERROR about asset render failed

```
TypeError:Cannot read property 'theme' of undefined;
```

I don't know why,maybe sth wrong about my hexo enviroment.
so I change

```
//index.js
var themeConfig = this.hexo.theme.config.less || {};
```

to

```
//index.js
var themeConfig = this.theme.config.less || {};
```

to fix it.

If there are any better ways to resolve this problem, please tell me. Thank U!

version
node v0.10.25
hexo v3.0.0
hexo-render-less v0.1.2