Update universitat-freiburg-geschichte.csl

Small corrections to match better the citation guidelines of Freiburg University
Update universitat-freiburg-geschichte.csl

Based on recommended changes on https://github.com/citation-style-language/styles/pull/555#issuecomment-17949491
Merge pull request #555 from glennfed/patch-1

Update universitat-freiburg-geschichte.csl