Added domain required for DDNS Updater.

blocklists/allowed-sites.txt

@@ -3,7 +3,7 @@
 # License: https://git.digitalvoid.me/steven/blocklists/src/branch/main/LICENSE
 # Syntax: Domains (without subdomains)
 
-# HomeLab
+# HomeLab Domains
 digitalvoid.me
 home.arpa
 
@@ -31,3 +31,6 @@ family.microsoft.com
 
 # Microsoft Rebates
 click.linksynergy.com
+
+# Self-Hosted App: DDNS Updater
+api.seeip.org