update degenerate polygon test
update degenerate polygon test

the expected behaviour here is that osmtogeojson does not return a
degenerate (multi)polygon.
it could in principle return just the way that is now sort of unused
but just as with an (untagged) node of a one-node-way we're going to
assume that those outlines aren't interesting enough.

tyrasd/osmtogeojson,scrool/osmtogeojson,tyrasd/osmtogeojson,scrool/osmtogeojson