Update rdoc dependency to version 3.8
Update rdoc dependency to version 3.8

jasnow/follow-all,jasnow/follow-all,codeforamerica/follow-all,BryanH/follow-all,jasnow/follow-all,BryanH/follow-all,BryanH/follow-all,codeforamerica/follow-all,codeforamerica/follow-all