message: Updated CHANGELOG for 1.5.2 release.
diff: # Changelog
  ## Unreleased
  -- Upgraded web-component-tester to v6.1.3 to address yarn installation issues.
  <!-- Add new, unreleased items here. -->
  +## v1.5.2 [08-26-2017]
  +- Upgraded web-component-tester to v6.1.3 to address yarn installation issues.
  +
  ## v1.5.1 [08-22-2017]
  - Upgraded web-component-tester to v6.1.2.
  