fix: fix broken links

README.md

@@ -249,13 +249,6 @@ Support this project by becoming a sponsor. Your logo will show up here with a l
 <a href="https://opencollective.com/casbin/sponsor/0/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/0/avatar.svg"></a>
 <a href="https://opencollective.com/casbin/sponsor/1/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/1/avatar.svg"></a>
 <a href="https://opencollective.com/casbin/sponsor/2/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/2/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/3/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/3/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/4/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/4/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/5/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/5/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/6/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/6/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/7/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/7/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/8/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/8/avatar.svg"></a>
-<a href="https://opencollective.com/casbin/sponsor/9/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/9/avatar.svg"></a>
 
 ## License