webpack4 : mini-css-extract-plugin and purifycss-webpack will :DeprecationWarning: Tapable.plugin is deprecated. Use new API on `.hooks` instead

[ruralist-siyi]

1. Check the version of package you are using. If it's not the newest version, update and try again (see changelog while updating!).
2. If the issue is still there, write a minimal project showing the problem and expected output.
3. Link to the project and mention Node version and OS in your report.

IMPORTANT! You should use Stack Overflow for support related questions.