Use bionic to run tests in travis-ci

Author: mayeut

.travis.yml

@@ -1,7 +1,8 @@
 os: linux
+dist: bionic
 language: python
 
-matrix:
+jobs:
   include:
   - python: "3.5"
   - python: "3.6"
@@ -16,7 +17,6 @@ matrix:
   - python: "3.7"
     env: LINTER=1
 
-sudo: required
 services:
   - docker