message: Fix diff link to 0.26.6 diff in CHANGELOG
diff: @@ -646,7 +646,8 @@ CHANGELOG entries missing. Please see [the diff][0.24.1].
  `FeeTable`. @cosmjs/cosmwasm has its own `FeeTable` with those properties.
  - @cosmjs/sdk38: Rename package to @cosmjs/launchpad.
  -[unreleased]: https://github.com/cosmos/cosmjs/compare/v0.26.5...HEAD
  +[unreleased]: https://github.com/cosmos/cosmjs/compare/v0.26.6...HEAD
  +[0.26.6]: https://github.com/cosmos/cosmjs/compare/v0.26.5...v0.26.6
  [0.26.5]: https://github.com/cosmos/cosmjs/compare/v0.26.4...v0.26.5
  [0.26.4]: https://github.com/cosmos/cosmjs/compare/v0.26.3...v0.26.4
  [0.26.3]: https://github.com/cosmos/cosmjs/compare/v0.26.2...v0.26.3
  