code: def dcos_version():
      
      url = _gen_url('dcos-metadata/dcos-version.json')
      response = dcos.http.request('get', url)
  
      if response.status_code == 200:
          return response.json()['version']
      else:
          return None
docs: Return the version of the running cluster.
      :return: DC/OS cluster version as a string