message: Prepare CLI v1.7.0-pre.13
diff: <!-- ## Unreleased -->
  <!-- Add new, unreleased items here. -->
  +## v1.7.0-pre.13 [04-19-2018]
  +* `init`
  + * Added the `polymer-3-starter-kit` template; a (prerelease) version of
  + Polymer Starter Kit, ported to Polymer 3.
  +
  ## v1.7.0-pre.12 [04-18-2018]
  * `serve`
  * Fix node module resolution for the case where the root package is served
  