changelog: fix links to 2.7.0/unreleased
-## Unreleased
+## [Unreleased]
## [2.7.0] - 2017-02-08
### Added
### Added
- Initial release
-[Unreleased]: https://github.com/travis-ci/worker/compare/v2.6.2...HEAD
+[Unreleased]: https://github.com/travis-ci/worker/compare/v2.7.0...HEAD
+[2.7.0]: https://github.com/travis-ci/worker/compare/v2.6.2...v2.7.0
[2.6.2]: https://github.com/travis-ci/worker/compare/v2.6.1...v2.6.2
[2.6.1]: https://github.com/travis-ci/worker/compare/v2.6.0...v2.6.1
[2.6.0]: https://github.com/travis-ci/worker/compare/v2.5.0...v2.6.0
