Add `mime-types` gem into the gemspec as a de
Add `mime-types` gem into the gemspec as a de

Closes #507
mrb/paperclip,freeslugs/paperclip,maintux/paperclip,sopheak-se/paperclip,bdewater/paperclip,agcantarelli/paperclip,felipemathies/paperclip,mehulkar/paperclip,medcat/paperclip,crowdtap/paperclip,soramugi/paperclip,jonathandean/paperclip_tod,Leadformance/paperclip,Flameeyes/paperclip,manorie/paperclip,fxposter/paperclip,crowdtap/paperclip,mrgilman/paperclip,zurb/paperclip,victorngkp/paperclip,onursarikaya/paperclip,dgynn/paperclip,tylerwillingham/paperclip,joshisa/paperclip,pcorliss/paperclip,ScotterC/paperclip,frankpinto/paperclip,mrgilman/paperclip,betesh/paperclip,pandamako/paperclip,gfvcastro/paperclip,raow/paperclip,yukas/paperclip,best-teacher/paperclip-old,joshisa/paperclip,Cohealo/paperclip,aditya01933/paperclip,carnivalmobile/paperclip,alexandrz/paperclip,hooroo/paperclip,medcat/paperclip,mrb/paperclip,freeslugs/paperclip,tylerwillingham/paperclip,tiegz/paperclip,keathley/paperclip,onursarikaya/paperclip,soramugi/paperclip,sopheak-se/paperclip,felipemathies/paperclip,howaboutwe/paperclip,Leadformance/paperclip,cmaion/paperclip,raow/paperclip,sideci-sample/sideci-sample-paperclip,Sporky023/paperclip,carnivalmobile/paperclip,rpbaptist/paperclip,greatbody/paperclip,danielwanja/paperclip,greatbody/paperclip,zurb/paperclip,degica/paperclip,justanshulsharma/paperclip,mdkalish/paperclip,cmaion/paperclip,keathley/paperclip,tiegz/paperclip,maintux/paperclip,degica/paperclip,frankpinto/paperclip,InesCARodrigues/paperclip,Cohealo/paperclip,alexandrz/paperclip,aditya01933/paperclip,mdkalish/paperclip,12spokes/paperclip,betesh/paperclip,ScotterC/paperclip,bdewater/paperclip,Sporky023/paperclip,justanshulsharma/paperclip,manorie/paperclip,pandamako/paperclip,dgynn/paperclip,InesCARodrigues/paperclip,victorngkp/paperclip,gfvcastro/paperclip,agcantarelli/paperclip,mehulkar/paperclip,rpbaptist/paperclip,kerrizor/paperclip