update travis base image to bionic (ubuntu 18.04)

mattip · mattip · commit a5140f19382a · 2021-07-12T21:21:46.000+03:00
diff --git a/.travis.yml b/.travis.yml
@@ -18,7 +18,7 @@ env:
 
 language: python
 sudo: required
-dist: xenial
+dist: bionic
 services: docker
 
 matrix:
