message: docs: improve changelog instructions
diff: v6 framework is now feature complete, the cli and material/cdk parts of the v6 release and other integrations are still
  in works and will be completed by the time we cut v6.0.0.
  +Please [file new issues](https://github.com/angular/angular/issues/new) at our issue tracker with as many details as
  +possible, and ideally also a include a good reproduction of the problem.
  +
  ### Bug Fixes
  * **bazel:** correct expected outs for external sources in ng_module ([#22755](https://github.com/angular/angular/issues/22755)) ([bfe077a](https://github.com/angular/angular/commit/bfe077a))
  @@ -22,7 +25,7 @@ in works and will be completed by the time we cut v6.0.0.
  <a name="6.0.0-beta.8"></a>
  -# [6.0.0-beta.8](https://github.com/angular/angular/compare/6.0.0-beta.7...6.0.0-beta.8) (2018-03-21)
  +# [6.0.0-beta.8](https://github.com/angular/angular/compare/6.0.0-beta.7...6.0.0-beta.8) (2018-03-16)
  ### Bug Fixes
  