Bump the required six version to prevent issues with dependencies
Bump the required six version to prevent issues with dependencies

roelvv/pyrax,naemono/pyrax,opsdisk/pyrax,mandx/pyrax,EdLeafe/pyrax,vikomall/pyrax,rackspace/pyrax,ddaeschler/pyrax,briancurtin/pyrax,sivel/pyrax,pratikmallya/pyrax