message: Fix Python min alignment
  This was accidentally deleted in:
diff: @@ -514,6 +514,13 @@ class Builder(object):
  """Finish finalizes a buffer, pointing to the given `rootTable`."""
  N.enforce_number(rootTable, N.UOffsetTFlags)
  + prepSize = N.UOffsetTFlags.bytewidth
  + if file_identifier is not None:
  + prepSize += N.Int32Flags.bytewidth
  + if sizePrefix:
  + prepSize += N.Int32Flags.bytewidth
  + self.Prep(self.minalign, prepSize)
  +
  if file_identifier is not None:
  self.Prep(N.UOffsetTFlags.bytewidth, encode.FILE_IDENTIFIER_LENGTH)
  