Updated SKIRT version number in PDF documentation
Updated SKIRT version number in PDF documentation

raesjo/SKIRTcorona,raesjo/SKIRT,SKIRT/SKIRT,raesjo/SKIRT,raesjo/SKIRT,raesjo/SKIRTcorona,raesjo/SKIRTcorona,SKIRT/SKIRT,SKIRT/SKIRT