(PDK-1501) Fix acceptance stages in Travis CI

Previously the Travis CI file was brought under PDK control, however the
sync.yml did not contain the stage settings for the Litmus jobs which meant
that they did not run.  This commit fixes that error and runs PDK Update again

.sync.yml

@@ -24,6 +24,7 @@
       - bundle exec rake litmus:acceptance:parallel
       services: docker
       sudo: required
+      stage: acceptance
     -
       bundler_args:
       dist: trusty
@@ -50,6 +51,7 @@
       - bundle exec rake litmus:acceptance:parallel
       services: docker
       sudo: required
+      stage: acceptance
     -
       bundler_args:
       dist: trusty
@@ -63,6 +65,7 @@
       - bundle exec rake litmus:acceptance:parallel
       services: docker
       sudo: required
+      stage: acceptance
 
 appveyor.yml:
   delete: true