h3 import calls are obsolete

[djconly85]

After updating to the latest version of gtfs_functions.py, I received ImportError: cannot import name 'geo_to_h3' from 'h3' when running from gtfs_functions import Feed.

I looked at the h3 version 3 documentation and it appears that both geo_to_h3 and k_ring no longer are valid for h3 version 4. I then confirmed that my update also updated h3 to be version 4.

As a test, made the following changes in this script:

• Changed all instances of geo_to_h3 to cell_to_latlng
• Changed all instances of k_ring to grid_disk

After making these changes, the module is now working as expected. I'm not sure if this is an issue all users have experienced but I figured I would flag it.