GH-4: Set default locale to en_US.UTF-8

Dockerfile

 FROM scratch
 ADD archlinux.tar /
+ENV LANG=en_US.UTF-8
 CMD ["/usr/bin/bash"]

Makefile

@@ -22,6 +22,7 @@ docker-image-test: docker-image
 	# Ensure that the image does not include a private key
 	! docker run --rm $(DOCKER_ORGANIZATION)/$(DOCKER_IMAGE) pacman-key --lsign-key pierre@archlinux.de
 	docker run --rm $(DOCKER_ORGANIZATION)/$(DOCKER_IMAGE) sh -c "/usr/bin/id -u http"
+	docker run --rm $(DOCKER_ORGANIZATION)/$(DOCKER_IMAGE) sh -c "/usr/bin/pacman -Syu --noconfirm grep && locale | grep -q UTF-8"
 
 ci-test:
 	docker run --rm --privileged --tmpfs=/tmp:exec --tmpfs=/run/shm -v /run/docker.sock:/run/docker.sock \