Update to babel 7 stable

[adamnoakes]

Updated to use preset-env with target of node 6 (i assume this is the lowest supported as jest won't run below 6). Ran the tests in a node 6 environment.

Not sure if this is major/ minor please advise and i'll update the changelog

[DangerCI]

Danger run resulted in 1 warning and 8 markdowns; to find out more, see the checks page.

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[cwright017]

#662 #627

[orta]

Aha, I see, so the runtime danger wouldn't support babel7 because of the require paths etc.

I think I'll go with a semantic version major bump here. Existing installs may have different behavior after updating.

Thanks!

[orta]

I'll handle the changelog with the release, don't worry about it 👍

[peril-staging]

Thanks for the PR @adamnoakes.

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 adamnoakes 🎉

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[peril-staging]

Thanks for the PR @adamnoakes.

This PR has been shipped in v4.0.0 - CHANGELOG.