Merge #1269: changelog: Fix link

6a37b2a changelog: Fix link (Tim Ruffing)

Pull request description:

Top commit has no ACKs.

Tree-SHA512: 70d50c8fe958a197eb527e51c6f8120609e3166d93bfc1bbec75a3cb565c406d5ba0e6d088a724dcfda422b6594abf53f507211946a0533515df371d5d2a91bf

Author: jonasnick

CHANGELOG.md

@@ -67,6 +67,7 @@ The number was given by the build system since the introduction of autotools in
 Therefore, this version number does not uniquely identify a set of source files.
 
 [unreleased]: https://github.com/bitcoin-core/secp256k1/compare/v0.3.0...HEAD
+[0.3.1]: https://github.com/bitcoin-core/secp256k1/compare/v0.3.0...v0.3.1
 [0.3.0]: https://github.com/bitcoin-core/secp256k1/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/bitcoin-core/secp256k1/compare/423b6d19d373f1224fd671a982584d7e7900bc93..v0.2.0
 [0.1.0]: https://github.com/bitcoin-core/secp256k1/commit/423b6d19d373f1224fd671a982584d7e7900bc93