travis-ci: upgrade dist of travis ci to ubuntu bionic. (#268)

xiaocang · web-flow · commit 28aea62120da · 2021-10-14T23:26:40.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 sudo: required
-dist: trusty
+dist: bionic
 
 os: linux
 
