Update the README to show the new URL for issues

This was forgotten when the repository was renamed from
"pg_permission" to "pg_permissions".

Reported by Devrim Gündüz.

Author: laurenz

README.md

@@ -178,5 +178,5 @@ Open an [issue][issue] on GitHub if you have problems or questions.
 For professional support, please contact [Cybertec][cybertec].
 
 
- [issue]: https://github.com/cybertec-postgresql/pg_permission/issues
+ [issue]: https://github.com/cybertec-postgresql/pg_permissions/issues
  [cybertec]: https://www.cybertec-postgresql.com/