Error: PostCSS plugin tailwindcss requires PostCSS 8

I installed the new tailwindcss version 2.0 and I’ve got the following error. I tried to uninstall postcss and tailwindcss but it does not work. Need help.

Module build failed (from ./node_modules/postcss-loader/src/index.js):
Error: PostCSS plugin tailwindcss requires PostCSS 8.
Migration guide for end-users:
https://github.com/postcss/postcss/wiki/PostCSS-8-for-end-users
    at Processor.normalize (/Users/niklas/Desktop/Privat/Projekte/nifoschool-frontend/node_modules/postcss-loader/node_modules/postcss/lib/processor.js:153:15)
    at new Processor (/Users/niklas/Desktop/Privat/Projekte/nifoschool-frontend/node_modules/postcss-loader/node_modules/postcss/lib/processor.js:56:25)
    at postcss (/Users/niklas/Desktop/Privat/Projekte/nifoschool-frontend/node_modules/postcss-loader/node_modules/postcss/lib/postcss.js:55:10)
    at /Users/niklas/Desktop/Privat/Projekte/nifoschool-frontend/node_modules/postcss-loader/src/index.js:140:12

 @ ./node_modules/vue-style-loader??ref--6-oneOf-1-0!./node_modules/css-loader/dist/cjs.js??ref--6-oneOf-1-1!./node_modules/vue-loader/lib/loaders/stylePostLoader.js!./node_modules/postcss-loader/src??ref--6-oneOf-1-2!./node_modules/cache-loader/dist/cjs.js??ref--0-0!./node_modules/vue-loader/lib??vue-loader-options!./src/components/util/SlideInfo.vue?vue&type=style&index=0&lang=css& 4:14-393 14:3-18:5 15:22-401
 @ ./src/components/util/SlideInfo.vue?vue&type=style&index=0&lang=css&
 @ ./src/components/util/SlideInfo.vue
 @ ./node_modules/cache-loader/dist/cjs.js??ref--12-0!./node_modules/babel-loader/lib!./node_modules/cache-loader/dist/cjs.js??ref--0-0!./node_modules/vue-loader/lib??vue-loader-options!./src/views/Grades.vue?vue&type=script&lang=js&
 @ ./src/views/Grades.vue?vue&type=script&lang=js&
 @ ./src/views/Grades.vue
 @ ./src/router/index.js
 @ ./src/main.js
 @ multi (webpack)-dev-server/client?http://172.20.12.3:8081&sockPath=/sockjs-node (webpack)/hot/dev-server.js ./src/main.js

Here is my package.json