Fix Copr build of kicad-doc on Fedora 26
Created by: aimylios
I just saw that the last Copr build 723372 failed on Fedora 26 due to a missing dependency. According to the log file, the Unicode::GCString module is not available.
I did not actually test this change locally (don't have a Fedora 26 installation available), but this is backported from the upstream SPEC and should (hopefully) not cause any further issues.