Remove deprecated babel 7 sourceMapTarget

[kesne]

This has been deprecated and Babel now throws an error even if this is passed as undefined.

[orta]

Cool! Sure thing

[peril-staging]

Thanks for the PR @kesne.

The Danger org conform to the Moya Community Continuity Guidelines, which means
that we want to offer any contributor the ability to control their destiny.

So, we've sent you an org invite - thanks 🎉

Generated by 🚫 dangerJS

[orta]

I've shipped this in a new release