docs(readme): f ix typo
docs(readme): f ix typo

`loader` over `use`.

faceyspacey/extract-css-chunks-webpack-plugin,lcxfs1991/extract-text-webpack-plugin,brightbytes/extract-css-chunks-webpack-plugin,shifteee/extract-text-webpack-plugin,lcxfs1991/extract-text-webpack-plugin,faceyspacey/extract-css-chunks-webpack-plugin,brightbytes/extract-css-chunks-webpack-plugin,shifteee/extract-text-webpack-plugin,webpack-contrib/extract-text-webpack-plugin,webpack-contrib/extract-text-webpack-plugin