message: add next release note to changelog
diff: [Want to contribute? Read our guide!](https://github.com/howdyai/botkit/blob/master/CONTRIBUTING.md)
  +# next_release
  +
  +These features can be found in master, but have not yet been officially released on npm.
  +
  +* Add support for Google Hangouts "card_clicked" event. [Thanks to @ouadie-lahdioui](https://github.com/howdyai/botkit/pull/1487) [NEEDS DOCS]()
  +
  # 0.6.17
  In addition to minor fixes, dependency version updates, and documentation updates, this version includes:
  