makefile: add Ubuntu Artful docker targets (.deb and ppa)

Artful Aardvark was released on 2017-10-19 and will be supported until 2018-07.

Makefile

@@ -246,6 +246,12 b' docker-ubuntu-zesty: contrib/docker/ubun'
 docker-ubuntu-zesty-ppa: contrib/docker/ubuntu-zesty
 	contrib/dockerdeb ubuntu zesty --source-only
 
+docker-ubuntu-artful: contrib/docker/ubuntu-artful
+	contrib/dockerdeb ubuntu artful
+
+docker-ubuntu-artful-ppa: contrib/docker/ubuntu-artful
+	contrib/dockerdeb ubuntu artful --source-only
+
 fedora20:
 	mkdir -p packages/fedora20
 	contrib/buildrpm
@@ -314,6 +320,7 b' linux-wheels-i686:'
 	docker-ubuntu-xenial docker-ubuntu-xenial-ppa \
 	docker-ubuntu-yakkety docker-ubuntu-yakkety-ppa \
 	docker-ubuntu-zesty docker-ubuntu-zesty-ppa \
+	docker-ubuntu-artful docker-ubuntu-artful-ppa \
 	fedora20 docker-fedora20 fedora21 docker-fedora21 \
 	centos5 docker-centos5 centos6 docker-centos6 centos7 docker-centos7 \
 	linux-wheels