[Provider AUTODNS] MX value does not contain 2 fields on 4.15.4 and newer

[angelprada]

Describe the bug
When update a zone in AUTODNS with MX records, it fails with error "MX value does not contain 2 fields".

******************** Domain: moebelhaus24.de
INFO#1: Domain "moebelhaus24.de" provider autodns Error: MX value does not contain 2 fields: ("smtp.google.com.")

Current line:
MX("@", 1, "smtp.google.com."),

To Reproduce
Steps to reproduce the behavior:

1. Preview or update a DNS zone with a MX record using dnscontrol 4.15.4 or newer

Expected behavior
Execute dnscontrol preview/push without fails

DNS Provider

• AUTODNS

Additional context
Fails in 4.15.4 and later, works with 4.15.3

[tlimoncelli]

CC @arnoschoon