Update babel, jest, webpack bits

[dholbach]

This should fix the handlebars and serialize-javascript security alerts on GH at least.

It also updates the node requirement (I think through the jest update this was necessary) - somebody should check if we can actually make the jump.

[dholbach]

https://circleci.com/gh/weaveworks/scope/14642 says

[1/5] Validating package.json...
error [email protected]: The engine "node" is incompatible with this module. Expected version "^10.19.0".
error Found incompatible module

I guess something like 56f2fac is needed here?

[bboreham]

I applaud your efforts, but really have no idea what changes are required when you move two major versions of Node.

I think you should have permissions to push a new build image; let me know if not.

[dholbach]

I think you should have permissions to push a new build image; let me know if not.

Looks like I don't. Can you help me out? My user is dholbach on Dockerhub too.

denied: requested access to the resource is denied

[fbarl]

Thanks @dholbach, LGTM! 🎉

Please don't forget to revert 795eaab after you merge.