bug in docker_plugin.py

[adf2007]

In paclair/plugins/docker_plugin.py，the function create_docker_image() might has a bug.

it should be like this:

Base docker image

    if matcher.group("domain") is None:
        if '/' in matcher.group("name"):
            return DockerImage(matcher.group("name"), self.__docker_hub,
                                tag=matcher.group("tag") or 'latest')
        else:
            return DockerImage("library/" + matcher.group("name"), self.__docker_hub,
                                tag=matcher.group("tag") or 'latest')

When I push a image like "nginx"，the DockerImage name should be "library/nginx".But when I push a image like "citizenstig/dvwa"，the DockerImage name should just be "citizenstig/dvwa" not "library/citizenstig/dvwa".