Use 'dist: xenial' in Travis to simplify configuration
Use 'dist: xenial' in Travis to simplify configuration

Allows using recent Python versions without sudo declarations.

Travis officially added support for Xenial on 2018-11-08.

https://blog.travis-ci.com/2018-11-08-xenial-release

twidi/django-decorator-include,jdufresne/django-decorator-include,jdufresne/django-decorator-include,twidi/django-decorator-include