Bump Travis to Go 1.7.3
Bump Travis to Go 1.7.3

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