def convert
      old = @hashes
      @hashes = Hash.new

      puts 'Warning: old JSON format detected, converting.'
      old.each {|i| add_hash(i[:id], i[:deletehash], 'unknown') }
      save
    end
def convert
      old = @hashes
      @hashes = Hash.new

      puts 'Warning: old JSON format detected, converting.'
      old.each {|i| add_hash(i[:id], i[:deletehash], 'unknown') }
      save
    end
Private: convert from old Json representation, filling in the missing data.
 Also print a warning message for the user.

 Returns nothing.