[logback-user] Timeout may frequently occurred on logback.qos.ch [IPv6]

[Takuma Tsutsumi]

Hi,

If using a user-agent that prefer IPv6 such as the Squid proxy, a timeout
may frequently occur on logback.qos.ch.

It seems to me that the IPv6 site does not exist.
 References:
  - http://ready.chair6.net/?url=https://logback.qos.ch
  - http://ipv6-test.com/validate.php

In addition, it seems that AAAA records may not be returned depending on
DNS query timing.
```
$ date; dig +noall +answer @8.8.8.8 logback.qos.ch aaaa
Thu Mar 30 22:34:03 DST 2017
logback.qos.ch.         279     IN      CNAME   yvo.qos.ch.
yvo.qos.ch.             279     IN      AAAA    2a02:121e:969:1:201:c0ff:
fe1c:5f7c

$ date; dig +noall +answer @8.8.8.8 logback.qos.ch aaaa
Thu Mar 30 22:34:05 DST 2017
logback.qos.ch.         299     IN      CNAME   te.qos.ch.
```

Would you please investigate this?

Regards,

Takuma Tsutsumi
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