Update security email addresses

Author: sagikazarmark

README.md

@@ -40,8 +40,7 @@ Please see our [contributing guide](http://docs.php-http.org/en/latest/developme
 
 ## Security
 
-If you discover any security related issues, please contact us at [security@httplug.io](mailto:security@httplug.io)
-or [security@php-http.org](mailto:security@php-http.org).
+If you discover any security related issues, please contact us at [security@php-http.org](mailto:security@php-http.org).
 
 
 ## License