chore(travis): check for doc directory before building extra docs
chore(travis): check for doc directory before building extra docs

hyperium/hyper,golddranks/hyper,markuskobler/hyper,yazaddaruvala/hyper,Twey/hyper,tshepang/hyper,nickgonzales/hyper,tshepang/hyper,golddranks/hyper,Twey/hyper,yazaddaruvala/hyper,hyperium/hyper,Keats/hyper,tshepang/hyper,markuskobler/hyper,Keats/hyper,Twey/hyper,hyperium/hyper,Keats/hyper,nickgonzales/hyper,golddranks/hyper,nickgonzales/hyper,markuskobler/hyper