fixed base urls for HereMaps

[chrstnbwnkl]

passes modified base urls for HereMaps' .directions(), isochrones() and matrix() methods to the instance's client

[nilsnolde]

You're probably not done yet, still my 2c. Also you can actually remove self.base_url entirely, no function will use it anymore

[nilsnolde]

the last minor stuff and we're good. no need for another review round. you can just fix the few things and merge yourself, I'll approve now.