Fix Compose 1.2 changelog link

Hardcode the release tag, so that:

- it goes straight to the changes for 1.2, not whatever the current
  version is

- it still works now that we've renamed CHANGES.md to CHANGELOG.md

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

docs/misc/release-notes.md

@@ -102,7 +102,7 @@ here](https://docs.docker.com/registry/spec/api/).
 
 For a complete list of compose patches, fixes, and other improvements, see the
 [changelog in the project
-repository](https://github.com/docker/compose/blob/master/CHANGES.md). The
+repository](https://github.com/docker/compose/blob/1.2.0/CHANGES.md). The
 project also makes a [set of release
 notes](https://github.com/docker/compose/releases/tag/1.2.0) on the project.