The docker remote api version need to be updated

[venkatamahesh]

The docker api version is v1.13 in "https://github.com/openstack/magnum/blob/master/specs/containers-service.rst#rest-api-impact", and the v1.13 link is getting error :404 not found as it is old version.
So the version is updated to new one.

[venkatamahesh (venkatamaheshkotha)]

We can update to latest version as "https://docs.docker.com/reference/api/docker_remote_api_v1.21/" .

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/219070

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/219070
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=41d08fe0003df743b3796567c14ba1ed6aa8be61
Submitter: Jenkins
Branch: master

commit 41d08fe0003df743b3796567c14ba1ed6aa8be61
Author: venkatamahesh <email address hidden>
Date: Tue Sep 1 06:07:30 2015 +0530

    Fix the link for Docker Remote API

    The link given to Docker API getting error as it
    is old version. So I removed the version extension
    and also named it as "Docker Remote API"

    Change-Id: If3d6ce2c74455a2d8c2c9fff51af1f5cbe330e76
    Closes-Bug: #1488708