config.js

Why can't we just use config.js instead of config.json but we can use config.env.js?

I wish to do this in my base config.js:

```
module.exports = {
  port: process.argv[2] || pkg.config.port || 7770
}
```

but I have to create 3 of them (config.development.js , config.staging.js , config.production.js ) 
