adds support for string arrays to arrayToLatLng

I had an issue calling getElevations with Bi-dimensional array of latitudes and longitudes that were in string and I was getting Uncaught RangeError: Maximum call stack size exceeded with arrayToLatLng. Since the original API accepts strings as well gmaps should support it too.

I could made the if to be `number` or `string`, but I think this is better. Your call.