Reimplement `eachParent`'s traversal (#117)
Reimplement `eachParent`'s traversal (#117)

Previously `eachParent` sliced the path all the way up to the empty string.

Practically this meant that calls to `eachParent` ended up _also_ taking
into consideration a `package.json` in the current working directory.

This implementation is based on the traversal code in `babel`.
ai/browserslist