def prune_members
      @holders = if lock_exists?
        holders = lock_content['Holders']
        return @holders = [] if holders.nil?
        holders = holders.keys
        holders & members
      else
        []
      end
    end
def prune_members
      @holders = if lock_exists?
        holders = lock_content['Holders']
        return @holders = [] if holders.nil?
        holders = holders.keys
        holders & members
      else
        []
      end
    end
Get the active members from the lock file, removing any _dead_ members.
 This is accomplished by using the contenders keys(`@members`) to get the
 list of all alive members.  So we can easily remove any nodes that don't
 appear in that list.