Fix typo in error msg
Make the longest_trip an int

Previously the longest_trip was rounded, but was still a float, resulting in
it being shown as '20.0 km' when it in reality was 19.8 km. This patch
change it to an int, so it should show up as '20 km', and will not give a
false impression of accuracy.
Merge pull request #30 from staalebk/fixup1

Fix typo in error msg, cast rounded number to int.