Negative values for Longitude 

Hi Gavin Rozzi,

Thank you for the great package "zipcodeR".

I used "geocode_zip" to get the lat and lon pair of the centroid of a given zip code. Latitude values are correct, however the longitude values are coming negative. So I have to multiply lon values by -1 to have the correct ones.

Can you please confirm if I am doing something wrong or if it is an issue with the code? Thank you!
