Remove aufs step from Makefile in favor of aufs provisioning provided by

official docker install script

Makefile

@@ -137,7 +137,7 @@ sigil:
 	wget -qO /tmp/sigil_latest.tgz ${SIGIL_URL}
 	tar xzf /tmp/sigil_latest.tgz -C /usr/local/bin
 
-docker: aufs
+docker:
 	apt-get install -qq -y curl
 	egrep -i "^docker" /etc/group || groupadd docker
 	usermod -aG docker dokku
@@ -149,11 +149,6 @@ endif
 	sleep 2 # give docker a moment i guess
 endif
 
-aufs:
-ifndef CI
-	lsmod | grep aufs || modprobe aufs || apt-get install -qq -y linux-image-extra-`uname -r` > /dev/null
-endif
-
 stack:
 ifeq ($(shell test -e /var/run/docker.sock && touch -c /var/run/docker.sock && echo $$?),0)
 ifdef BUILD_STACK