update contributors to add @mattfora
update contributors to add @mattfora

michaelMinar/limbo,kylemsguy/limbo,shawnsi/limbo,NUKnightLab/slask,Marclass/limbo,dorian1453/limbo,sentinelleader/limbo,TetraEtc/limbo,palachu/sdbot,mmisiewicz/slask,rizaon/limbo,TetraEtc/limbo,llimllib/limbo,wmv/slackbot-python,llimllib/limbo,uilab-github/slask,ruhee/limbo,uilab-github/slask,UnILabKAIST/slask,serverdensity/sdbot,signalnine/alanabot,freshbooks/limbo