Upgrade net/nmsg to version 0.13.0:

• Sanitize JSON UTF-8 output. Invalid UTF-8 sequences are replaced with the replacement code point U+FFFD.
• Run msgmod 'load' method when loading a message from raw payload or duplicating an existing message.
• dnstap msgmod: format query_zone in human-readable format.

Sponsored by: Farsight Security, Inc.