your webserver on www.igniterealtime.org (and download.igniterealtime.org, maybe others) is configured wrong:
--2016-12-01 17:30:40-- https://www.igniterealtime.org/downloadServlet?filename=openfire/openfire_4.0.4_ all.deb
Resolving www.igniterealtime.org (www.igniterealtime.org)... 188.8.131.52
Connecting to www.igniterealtime.org (www.igniterealtime.org)|184.108.40.206|:443... connected.
ERROR: The certificate of `www.igniterealtime.org' is not trusted.
The problem is with the intermediate certs of the Let's Encrypt certificate, please see https://www.ssllabs.com/ssltest/analyze.html?d=www.igniterealtime.org