hierarchy_fix: prevent superseded parent from replacing self-references in the hierarchy

[missinglink]

following on from #21 I caught a fairly uncommon case where a document A has a parent X superseded by Y.
The problem is that if A & Y have the same placetype then the self-reference was being incorrectly replaced.

A = locality
A.hierarchy[0].localadmin_id = X

X (localadmin) is superseded by Y (locality)

A.hierarchy[0].locality_id MUST still equal A, not Y

eg: whosonfirst-data/whosonfirst-data-admin-ca@505cc0e#diff-7e8b7130e6db85a8e6d8fad892353ee8

[missinglink]

npm publish
+ @whosonfirst/wof@0.29.0

[orangejulius]

It's funny reading each of your PRs here as you find more and more "interesting" edge cases and uncommon issues. Seems like WOF data is very inherently hard to keep consistent, even though its hierarchy is powerful.

Good to see we are at least chipping away at it with some helpful automation :)