add some properties in returned error

Hi,

A little addition to send an error with a `fileName` property. Exactly like `gulp-uglify` here :
https://github.com/terinjokes/gulp-uglify/blob/master/index.js#L55

It's usefull if you want notice where the error is, example:

```js
var w = whitespace();
w.on('error', function(err) {
  console.log('CSS Whitespace error with file', err.fileName);
  w.end();
})
```

I also return `plugin` exactly like `gutil.PluginError` does, example here:
https://github.com/sindresorhus/gulp-rework/blob/master/index.js#L30

I also updated `gulp-util` dependency to the latest `3.0`