Merge branch 'update_upgrade_document' into 'master'

Update Upgrade from 6.6 ce to ee document

Use correct assets commands.

doc/update/6.6-ce-to-ee.md

@@ -44,7 +44,7 @@ sudo -u git -H bundle install --without development test postgres --deployment
 sudo -u git -H bundle install --without development test mysql --deployment
 
 sudo -u git -H bundle exec rake db:migrate RAILS_ENV=production
-sudo -u git -H bundle exec rake assets:precompile RAILS_ENV=production
+sudo -u git -H bundle exec rake assets:clean assets:precompile cache:clear RAILS_ENV=production
 ```
 
 ### 5. Update Init script