Fix known blank page issue in Safari

There's been a weird edge-case caching issue with Express apps ever since Safari 7 where users can see blank pages.

This change adds the "jumanji" dependency to fix the issue. Details about the issue are in its README: 
https://github.com/Dakuan/jumanji

**Note:** We have to wait for `jumanji` to be approved/whitelisted before we can merge this PR.