.travis: use bionic

ph4r05 · ph4r05 · commit 9a5fbe7e6cc1 · 2020-04-20T02:22:32.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -3,7 +3,7 @@ language: cpp
 
 # Use container based infrastructure for Travis
 sudo: false
-dist: xenial
+dist: bionic
 
 cache:
   directories:
