After update yarn.lock causes error during ibexa:encore:compile

Steps:

1. Install any edition v4.1.5.
2. Follow update to v4.2.0.
3. At the end examine result of composer run post-update-cmd command.

Actual result: Error occurs

!!    ERR  [webpack-cli] Failed to load '/Users/michalszoltysek/Projects/workspace/test_cnt_331/webpack.config.js' config
!!    ERR  [webpack-cli] Error: Cannot find module 'postcss-import'

Expected result: Command finishes cleanly without workarounds.

Remarks: Workaround is to remove yarn.lock and repeat command.