message: update changelog to prepare for v0.18.0-alpha.9 release
diff: ## Upcoming
  +
  +## v0.18.0-alpha.9
  +
  - Fixed a bug where `polymer init` would crash if run from a folder with a
  package.json that's missing a name property. https://github.com/Polymer/polymer-cli/issues/186
  +- Fixed a bug where `polymer build` wouldn't analyze behaviors correctly.
  +- Fixed a bug where `polymer test` would complain about the version of wct it was bundled with.
  +- Updated dependencies.
  ## v0.18.0-alpha.8
  