Optimize travis config

Signed-off-by: Alexey Stepanov <penguinolog@gmail.com>

Author: penguinolog

.travis.yml

@@ -1,6 +1,8 @@
-sudo: false
 language: python
 os: linux
+dist: xenial
+sudo: true
+
 install:
 - &upgrade_python_toolset pip install --upgrade pip setuptools wheel
 - &install_test_deps pip install --upgrade pytest pytest-sugar
@@ -14,8 +16,6 @@ _python:
 - &python37
   name: "Python 3.7"
   python: 3.7
-  dist: xenial
-  sudo: true
 
 _helpers:
 - &install_cython pip install --upgrade Cython