message: Fix signature spec link
diff: # Mina signer
  -This crate provides an API and framework for Mina signing. It follows the algorithm outlined in the [Mina Signature Specification](https://github.com/MinaProtocol/mina/blob/develop/docs/specs/signatures/description.md).
  +This crate provides an API and framework for Mina signing. It follows the algorithm outlined in the [Mina Signature Specification](https://github.com/MinaProtocol/mina/blob/master/docs/specs/signatures/description.md).
  ## Simple interface
  