def stripped_size
      80 + Bitcoin.pack_var_int(transactions.size).bytesize +
          transactions.inject(0){|sum, tx| sum + tx.serialize_old_format.bytesize}
    end
def stripped_size
      80 + Bitcoin.pack_var_int(transactions.size).bytesize +
          transactions.inject(0){|sum, tx| sum + tx.serialize_old_format.bytesize}
    end
calculate base size (not include witness data.)