Remove duplicate line in exec_run documentation
Remove duplicate line in exec_run documentation

Signed-off-by: Mehdi Bayazee <b8b661109ce1fbc44955567e6189c693aa40eeb3@gmail.com>

vpetersson/docker-py,funkyfuture/docker-py,dimaspivak/docker-py,vdemeester/docker-py,youhong316/docker-py,vdemeester/docker-py,funkyfuture/docker-py,youhong316/docker-py,docker/docker-py,auready/docker-py,docker/docker-py,auready/docker-py,dimaspivak/docker-py,kaiyou/docker-py,kaiyou/docker-py,vpetersson/docker-py