Fix OpenLocationCode. recover_nearest implementation to pass tests

bryanjos

The OpenLocationCode. recover_nearest implementation seems to be broken in some way. I implemented most of this library by looking at the [ruby implementation of open location code here](https://github.com/google/open-location-code/blob/master/ruby/lib/plus_codes/open_location_code.rb#L144) Google supplies CSVs for testing implementations of open location code. The [shorten](https://github.com/bryanjos/open_location_code/blob/master/test/open_location_code_test.exs#L75) test currently fails. I have checked the implementation a couple of times to see if I can find the issue but have not been able to at this point.

oohnoitz

I compared the calculations and found that `latitude` was slightly off after doing `decode!/1`. It seems that there are some instances where `integer division` is being done instead of returning a decimal value. I think it might be worth double checking all division operations to make sure that they are correct.