util/packer: Update Docker apt URL
util/packer: Update Docker apt URL

Signed-off-by: Lewis Marshall <748e1641a368164906d4a0c0e3965345453dcc93@lmars.net>

josephglanville/flynn,whouses/flynn,shads196770/flynn,jzila/flynn,justintung/flynn,supermario/flynn,schatt/flynn,josephglanville/flynn,schatt/flynn,TribeMedia/flynn,tonicbupt/flynn,rikur/flynn,benbjohnson/flynn,pkdevbox/flynn,rikur/flynn,pkdevbox/flynn,flynn/flynn,schatt/flynn,philiplb/flynn,shads196770/flynn,rikur/flynn,philiplb/flynn,jzila/flynn,shads196770/flynn,ozum/flynn,jzila/flynn,philiplb/flynn,schatt/flynn,kgrz/flynn,TribeMedia/flynn,josephglanville/flynn,benbjohnson/flynn,technosophos/flynn,whouses/flynn,supermario/flynn,rikur/flynn,kgrz/flynn,felixrieseberg/flynn,kgrz/flynn,TribeMedia/flynn,schatt/flynn,rikur/flynn,kgrz/flynn,Brandywine2161/flynn,tonicbupt/flynn,lmars/flynn,Brandywine2161/flynn,GrimDerp/flynn,clifff/flynn,jzila/flynn,GrimDerp/flynn,justintung/flynn,justintung/flynn,clifff/flynn,lmars/flynn,felixrieseberg/flynn,technosophos/flynn,flynn/flynn,philiplb/flynn,GrimDerp/flynn,shads196770/flynn,justintung/flynn,ozum/flynn,supermario/flynn,Brandywine2161/flynn,flynn/flynn,jzila/flynn,ozum/flynn,Brandywine2161/flynn,flynn/flynn,kgrz/flynn,shads196770/flynn,benbjohnson/flynn,technosophos/flynn,ozum/flynn,TribeMedia/flynn,josephglanville/flynn,shads196770/flynn,clifff/flynn,GrimDerp/flynn,whouses/flynn,schatt/flynn,tonicbupt/flynn,rikur/flynn,tonicbupt/flynn,tonicbupt/flynn,benbjohnson/flynn,josephglanville/flynn,Brandywine2161/flynn,technosophos/flynn,clifff/flynn,TribeMedia/flynn,felixrieseberg/flynn,pkdevbox/flynn,flynn/flynn,whouses/flynn,kgrz/flynn,jzila/flynn,pkdevbox/flynn,supermario/flynn,whouses/flynn,TribeMedia/flynn,clifff/flynn,felixrieseberg/flynn,philiplb/flynn,lmars/flynn,GrimDerp/flynn,supermario/flynn,benbjohnson/flynn,lmars/flynn,whouses/flynn,Brandywine2161/flynn,justintung/flynn,benbjohnson/flynn,pkdevbox/flynn,lmars/flynn,justintung/flynn,josephglanville/flynn,ozum/flynn,clifff/flynn,felixrieseberg/flynn,GrimDerp/flynn,pkdevbox/flynn,supermario/flynn,ozum/flynn,technosophos/flynn