Error in new version of rebuild scripts

[davenquinn]

I have already found an error with my recent changes to the Macrostrat rebuild scripts (#231).

In my local version, with the new rebuild scripts applied, the t_int of unit 41112 is mapped to some random biozone.

In dev, the same unit is correctly mapped to the top of the Tonian.
https://dev.macrostrat.org/projects/10/columns/2150#unit=41112

This is probably an issue in the lookup_units script.