removed a f-string for older Python 3 compatibility and added encoding comment for Python 2
removed a f-string for older Python 3 compatibility and added encoding comment for Python 2

scikit-rf/scikit-rf,temmeand/scikit-rf,temmeand/scikit-rf,scikit-rf/scikit-rf,jhillairet/scikit-rf,jhillairet/scikit-rf,jhillairet/scikit-rf,temmeand/scikit-rf