The shortcode plugin attempts to contact the IP 148.66.138.168. Why?

Thank you for the fantastic plugin.

Our webserver is installed behind a firewall and outgoing connections are being restricted.
After buying and installing the shortcode plugin,
the system often attempts to contact a system under the IP “148.66.138.168”, port 80, using the HTTP protocol.
Why is this being attempted?
Is this configurable?
I’m guessing that there’?s a legitimate reason for that connection to happen.
What is the DNS name of the contacted server, so that we can allow the connection
in our firewall?

Thank you very much.

Best regards,

Christoph