Replace deprecated try! with ?

[andrewgy8]

As of 1.39, the try! macro is deprecated

[andrewgy8]

BTW, I ran all tests locally and this was the output:

running 9 tests
test categorize::test_accessible ... ok
test categorize::test_update ... ok
test categorize::test_normalize ... ok
test models::test_distance ... ok
test models::test_as_wkt ... ok
test reader::test_count_nodes ... ok
test reader::test_wrong_file ... ok
test reader::test_split ... ok
test reader::test_real_all ... ok

test result: ok. 9 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/debug/deps/osm4routing-d3efa1cde45131ef

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

   Doc-tests osm4routing

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

[Tristramg]

Thank you very much for this contribution!