Updating PIWIK and iptables

I recently setup iptables on my server and ever since face problems when trying to update PIWIK to 2.14.

The error message is

curl_exec: couldn't connect to host. Hostname requested was: builds.piwik.org

while I can access

curl builds.piwik.org

from the command line.

Also - the update via the http connection does work, over the https connection fails.

So I suppose it is more a problem with the secure connection.
Help would be really appriciated.