fix(docs): CHANGELOG for v0.8.0 (#74)

Fixes a missed ref

Author: nuzzles

CHANGELOG.md

@@ -163,7 +163,8 @@ This release has an [MSRV][] of 1.75.
 [#6]: https://github.com/linebender/vello_svg/pull/6
 [#1]: https://github.com/linebender/vello_svg/pull/1
 
-[Unreleased]: https://github.com/linebender/vello_svg/compare/v0.7.1...HEAD
+[Unreleased]: https://github.com/linebender/vello_svg/compare/v0.8.0...HEAD
+[0.8.0]: https://github.com/linebender/vello_svg/compare/v0.7.1...v0.8.0
 [0.7.1]: https://github.com/linebender/vello_svg/compare/v0.7.0...v0.7.1
 [0.7.0]: https://github.com/linebender/vello_svg/compare/v0.6.0...v0.7.0
 [0.6.0]: https://github.com/linebender/vello_svg/compare/v0.5.0...v0.6.0