Fix Travis CI settings and deprecated 'sudo: false'

There is no need to set the 'sudo: false' anymore. This enabled
a container based CI that is not used anymore in Travis CI. The
Xenial based Travis builds are always VM based builds and there
is no need or use to define the 'sudo: false' anymore.

[1]
https://stackoverflow.com/a/53346787
https://changelog.travis-ci.com/the-container-based-build-environment-is-fully-deprecated-84517

Signed-off-by: Heikki Laaksonen <laaksonen.heikki.j@gmail.com>

.travis.yml

@@ -1,5 +1,3 @@
-sudo: false
-
 language: python
 dist: xenial
 cache: pip