update jest to the latest version

[artra]

Some new methods are missing in the 20.x version

[Timer]

Please see #3124; we cannot release Jest without a breaking version so this is postponed until v2.0.0.

[artra]

eject everywhere 😢

[gaearon]

It shipped in 2.0.
https://reactjs.org/blog/2018/10/01/create-react-app-v2.html