code: def all_write!
        will_change!
        permissions.keys.each do |perm|
          permissions[perm].write! true
        end
      end
docs: Grants write permission on all existing users and roles attached to this object.
   @example
    object.acl
    #    { "*":          { "read" : true },
    #      "3KmCvT7Zsb": { "read" : true, "write": true },
    #      "role:Admins": { "write": true }
    #     }
    object.acl.all_write!
    # Outcome:
    #    { "*":          { "read" : true, "write": true },
    #      "3KmCvT7Zsb": { "read" : true, "write": true },
    #      "role:Admins": { "write": true }
    #     }
   @version 1.7.2
   @return [Array] list of ACL keys