Does not work with browserify -r option

Below is my `test.js` :

```
var fs = require('fs');
var html = fs.readFileSync(__dirname + '/widget.html', 'utf8');
module.exports = Test;
function Test () {};
```

Use brfs without `-r` :

```
browserify -t brfs ./test.js
```

will get correctly compiled string :

```
var html = "\n \n \n";
```

But use with `-r` :

```
browserify -t brfs -r ./test.js:test
```

`fs` code will not be compiled :

```
var html = fs.readFileSync(__dirname + '/widget.html', 'utf8');
```