restore webpack defaults for managed/immutablePaths (#25250)
restore webpack defaults for managed/immutablePaths (#25250)

Due to bundling of webpack the default values can't be correctly detected
This restores the webpack defaults
azukaru/next.js,zeit/next.js,zeit/next.js,JeromeFitz/next.js,azukaru/next.js,JeromeFitz/next.js,JeromeFitz/next.js,flybayer/next.js,azukaru/next.js,zeit/next.js,azukaru/next.js,flybayer/next.js,flybayer/next.js,JeromeFitz/next.js,flybayer/next.js