Remove completed issue

from "Contributions" subsection

README.md

@@ -6,7 +6,7 @@ If you would like to get a grant to create PLUME applications or help to fix bug
 
 ## Contributions
 
-If you'd like to contribute, we offer $50 bounties in Eth/DAI for resolving any of the bugs in our issues! Each of them is quite small. That includes [#28](https://github.com/plume-sig/zk-nullifier-sig/issues/28), [#24](https://github.com/plume-sig/zk-nullifier-sig/issues/24), [#22](https://github.com/plume-sig/zk-nullifier-sig/issues/22), [#20](https://github.com/plume-sig/zk-nullifier-sig/issues/20), [#19](https://github.com/plume-sig/zk-nullifier-sig/issues/19), [#18](https://github.com/plume-sig/zk-nullifier-sig/issues/18), [#17](https://github.com/plume-sig/zk-nullifier-sig/issues/17), [#16](https://github.com/plume-sig/zk-nullifier-sig/issues/16), [#15](https://github.com/plume-sig/zk-nullifier-sig/issues/15), [#14](https://github.com/plume-sig/zk-nullifier-sig/issues/14),and [#13](https://github.com/plume-sig/zk-nullifier-sig/issues/13).
+If you'd like to contribute, we offer $50 bounties in Eth/DAI for resolving any of the bugs in our issues! Each of them is quite small. That includes [#28](https://github.com/plume-sig/zk-nullifier-sig/issues/28), [#24](https://github.com/plume-sig/zk-nullifier-sig/issues/24), [#22](https://github.com/plume-sig/zk-nullifier-sig/issues/22), [#20](https://github.com/plume-sig/zk-nullifier-sig/issues/20), [#19](https://github.com/plume-sig/zk-nullifier-sig/issues/19), [#17](https://github.com/plume-sig/zk-nullifier-sig/issues/17), [#16](https://github.com/plume-sig/zk-nullifier-sig/issues/16), [#15](https://github.com/plume-sig/zk-nullifier-sig/issues/15), [#14](https://github.com/plume-sig/zk-nullifier-sig/issues/14),and [#13](https://github.com/plume-sig/zk-nullifier-sig/issues/13).
 
 ## Implementations