download_service: use URI.open to open uri
download_service: use URI.open to open uri

Otherwise we get an annoying deprecation warning.

git/git-scm.com,Mokolea/git-scm.com,git/git-scm.com,Mokolea/git-scm.com,Mokolea/git-scm.com,mosoft521/gitscm-next,mosoft521/gitscm-next,git/git-scm.com,mosoft521/gitscm-next,Mokolea/git-scm.com,git/git-scm.com,mosoft521/gitscm-next