fix(headers): use $crate when referring to hyper modules on macros
fix(headers): use $crate when referring to hyper modules on macros

This adds a $crate variable missed by de1be6726

Closes #323

youprofit/hyper,mikedilger/hyper,lame-nickname/hyper,nickgonzales/hyper,nickgonzales/hyper,golddranks/hyper,reem/hyper,tshepang/hyper,markuskobler/hyper,fengsp/hyper,manuel-woelker/hyper,markuskobler/hyper,nstoddard/hyper,Twey/hyper,golddranks/hyper,rschulman/hyper,mneumann/hyper,softprops/hyper,tshepang/hyper,hyperium/hyper,steveklabnik/hyper,Twey/hyper,mlalic/hyper,tshepang/hyper,mre/hyper,bheesham/hyper,sfackler/hyper,TimNN/hyper,tempbottle/hyper,achanda/hyper,erickt/hyper,fuchsnj/hyper,mlalic/hyper,Twey/hyper,clatour/hyper,Ryman/hyper,hannobraun/hyper,hyperium/hyper,mfeckie/hyper,fhahn/hyper,jmmaranan/hyper,markuskobler/hyper,pyfisch/hyper,peterhj/hyper,yazaddaruvala/hyper,hannobraun/hyper,golddranks/hyper,ianks/hyper,yangxingpping/hyper,Keats/hyper,giftcards/hyper,yazaddaruvala/hyper,Keats/hyper,mitsuhiko/hyper,nstoddard/hyper,Keats/hyper,hyperium/hyper,huonw/hyper,hannobraun/hyper,nickgonzales/hyper,bonifaido/hyper