Require Node.js 10

[realityking]

I'm not sure if you're happy with the change I've made to how semver is used. Please let me know if you want that changed back to the satisfies function.

[realityking]

xo is failing because of the helper/util.js file being imported in the tests. How do you want to handle that?

[sindresorhus]

Thanks. I'll handle the thing. I don't plan to release this yet though as it's not worth doing a breaking change just for this. Also, for users that can target Node.js 10, they can just use the native option.

[realityking]

Well not those packages that supper Node >=10<10.12 but I understand that the semver bump is not worth the release.