Update universite-de-liege-histoire.csl

1. Removed the comma as sort-separator and replaced it by a space. Change required as to reflect University of Liège Department of History citation's rules. (cf. http://www.schist.ulg.ac.be/biblio/trav.htm )
2. Fixed macro "author" (shorter & "editors" not redundant) as suggested by rmzelle & adam3smith (Thanks to them !)

NB: validates on https://simonster.github.io/csl-validator.js/