Changed get_map zoom calculation to get min zoom level

[metanoid]

Sometimes, if the bounding box is either very wide or very tall, the zoom level chosen in get_map is too high (i.e. too zoomed in). I think the right behaviour is to choose the zoom level that captures the entire bounding box.

[dkahle]

Thanks, could you make a change in the NEWS file as well, please?

[espinielli]

Thanks for this. I am using the fix in a local copy of the function. Any chance to have it in next CRAN version? (If I can ask, when? :smile: )