cssDest has no affect on the generated css/scss file
Hi @jeerbl 

My goal is to generate the scss file to a different directory and rename it to _icons.scss. I'm trying to achieve this with cssDest as described [here](https://github.com/sunflowerdeath/webfonts-generator#cssdest), but the scss file stays in the same directory and keeps the same name as the webfonts do. I also tried this with scssFile: false, but the behaviour with css is the same. My webpack config is as followed:

package.json:
```
{
  "name": "Webfonts-Loader-Test",
  "license": "MIT",
  "dependencies": {
    "css-loader": "*",
    "mini-css-extract-plugin": "^0.7.0",
    "webfonts-loader": "^4.4.0",
    "webpack": "*",
    "webpack-cli": "^3.3.1",
    "webpack-merge": "*"
  }
}
```

webpack.config.js:
```
const path = require('path');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
    entry: [
        './entry.js'
    ],
    output: {
        path: path.resolve(__dirname, 'dist'),
        publicPath: '/',
        filename: 'bundle.js'
    },
    module: {
        rules: [
            {
                test: /\icons\.js$/,
                use: [
                    MiniCssExtractPlugin.loader,
                    'css-loader',
                    'webfonts-loader'
                ]
            }
        ]
    },
    plugins: [
        new MiniCssExtractPlugin({
            filename: 'styles.css'
        })
    ]
};
```

icons.js:
```
module.exports = {
    files: [
        './icons/*.svg'
    ],
    fontName: 'Icons',
    classPrefix: 'icon-',
    baseSelector: '.icon',
    embed: true,
    scssFile: true,
    writeFiles: true,
    types: ['woff2', 'ttf'],
    dest: './dist/fonts/',
    cssFontsUrl: '/dist/fonts/',
    cssDest: './dist/scss/_icons.scss'
};
```

Any ideas on how to achieve this?

Cheers,
Michael