SupportLeanbackShowcase: bring gradle, build tools, lib up to date am: 15f5a3351f
am: dcba115971

* commit 'dcba115971d8b2bb313760b87735629de4a8dd9b':
  SupportLeanbackShowcase: bring gradle, build tools, lib up to date

Change-Id: Ia4291893d7339fdfe92cb14b4b3db98e2f29781c