Fix command for getting hugo in CONTRIBUTING.md
Fix command for getting hugo in CONTRIBUTING.md

mayah/hugo,tubo028/hugo,fedelibre/hugo,MarkDBlackwell/hugo,bogem/hugo,mdhender/hugo,Zenithar/hugo,bogem/hugo,mdhender/hugo,mitchchn/hugo,anthonyfok/hugo,anthonyfok/hugo,mitchchn/hugo,fedelibre/hugo,jygastaud/hugo,MarkDBlackwell/hugo,gohugoio/hugo,fedelibre/hugo,digitalcraftsman/hugo,tubo028/hugo,gohugoio/hugo,ffrizzo/hugo,fedelibre/hugo,ffrizzo/hugo,gohugoio/hugo,mayah/hugo,Zenithar/hugo,mdhender/hugo,jygastaud/hugo,mdhender/hugo,anthonyfok/hugo,digitalcraftsman/hugo