loadConfigFile() {
        let postcssrc = require('postcss-load-config');

        try {
            this.plugins = [...this.plugins, ...postcssrc.sync().plugins];
        } catch (e) {
            // No postcss.config.js file exists.
        }
    }
Load the user's postcss.config.js file, if any.

@deprecated postcss-loader already does this on its own