geocoder.reverseGeocode does not accept zeros

[rbeitra]

If you try to do a reverseGeocode on a location on the prime meridian or the equator (lat===0 or lon===0) you get an error because of the input validation here:

https://github.com/wyattdanger/geocoder/blob/578e795de17ad874f0e08a49ae749d84b1145779/index.js#L71

if(undefined !== lat || undefined !== lon){}" would fix this!