docs: update contact email address (#966)

Author: morremeyer

SECURITY.md

@@ -2,7 +2,7 @@
 
 ## Reporting a Vulnerability
 
-Please do not open an issue if you find a vulnerability. Send an email to envelope-zero@maurice-meyer.de and a maintainer will get in touch with you as soon as possible. This might take up to 72 hours.
+Please do not open an issue if you find a vulnerability. Send an email to security@envelope-zero.org and a maintainer will get in touch with you as soon as possible. This might take up to 72 hours.
 
 You will be kept up to date with all developments via email.