Update Dockerfile to use golang:1.6 base image
Update Dockerfile to use golang:1.6 base image

Hugo has been confirmed which runs on Golang 1.6, as travis uses 1.6
vesion. Dockerfile must be consistend with it so it has to use golang:1.6
as base image than golang:1.5

mdhender/hugo,digitalcraftsman/hugo,fedelibre/hugo,abourget/hugo,bogem/hugo,fedelibre/hugo,anthonyfok/hugo,mitchchn/hugo,tubo028/hugo,gohugoio/hugo,soundrussian/hugo,mdhender/hugo,sprig/hugo,soundrussian/hugo,vbatoufflet/hugo,mayah/hugo,mdhender/hugo,ffrizzo/hugo,vbatoufflet/hugo,anthonyfok/hugo,ffrizzo/hugo,mdhender/hugo,MarkDBlackwell/hugo,bogem/hugo,gohugoio/hugo,abourget/hugo,Zenithar/hugo,fedelibre/hugo,sprig/hugo,fedelibre/hugo,jygastaud/hugo,Zenithar/hugo,mayah/hugo,gohugoio/hugo,melo/hugo,anthonyfok/hugo,MarkDBlackwell/hugo,mitchchn/hugo,tubo028/hugo,tischda/hugo,jygastaud/hugo,melo/hugo,digitalcraftsman/hugo,tischda/hugo