dns/dnscrypt-proxy2: update 2.0.18 to 2.0.19

• The value for netprobe_timeout was read from the command-line, but not from the configuration file any more. This is a regression introduced in the previous version, that has been fixed;
• The default value for netprobe timeouts has been raised to 60 seconds;
• A hash of the body is added to query parameters when sending DoH queries with the POST method in order to work around badly configured proxies.

https://raw.githubusercontent.com/jedisct1/dnscrypt-proxy/2.0.19/ChangeLog

Approved by: araujo (mentor)
Differential Revision: https://reviews.freebsd.org/D18341