Remove unnecessary sudo keys from the travis file

- sudo: false -- is going away
- sudo: required -- is now the default behavior

Author: thicolares

.travis.yml

@@ -1,8 +1,6 @@
 language: python
 python: 3.6
 
-sudo: false
-
 matrix:
   include:
     - python: 2.7
@@ -16,7 +14,6 @@ matrix:
     - python: 3.7
       env: TOXENV=py37
       dist: xenial
-      sudo: required
     - python: pypy
       env: TOXENV=pypy
     - env: TOXENV=pep8