.config.js

// my webpack.config.js
{
  test: /\.s?css$/,
  use: ExtractTextPlugin.extract({
    fallback: 'style-loader',
    use: [
      {
        loader: 'css-loader',
        options: {
          minimize: true,
          importLoaders: 1
        }
      },
      {
        loader: 'postcss-loader',
        options: {
          ident: 'postcss',
          config: `./postcss.config.js`
        }
      },
      {
        loader: 'sass-loader'
      }
    ]
  })
}

//my postcss.config.js
module.exports = {
    plugins: {
        'postcss-flexbugs-fixes': {},
        'autoprefixer': {}
    }
};

/**
Produces the error "PostCSS Loader Invalid Options options.config should be object"

I've tried changing it to a require(./postcss.config.js) which then produced the error:
"PostCSS Loader Invalid Options options.config['plugins'] should NOT have additional properties"
**/