fix zip code selection by writing a better predicate

[cole-brokamp]

The zipcodes currently are retained even if they only touch with the county, but these should be excluded:

Change would go here for e.g., the 2010 tract data:

https://github.com/geomarker-io/cincy/blob/a3f5f8c255d9d5bc8e2475d1b04f72f55e596c03/data-raw/make_data.R#L24