Go back to bionic distro.

Author: paulofaria

.travis.yml

@@ -9,7 +9,7 @@ matrix:
       osx_image: xcode11
     - os: linux
       env: JOB=SwiftPM_linux
-      dist: focal
+      dist: bionic
       sudo: required
       install:
         -  travis_retry eval "$(curl -sL https://gist.githubusercontent.com/kylef/5c0475ff02b7c7671d2a/raw/9f442512a46d7a2af7b850d65a7e9bd31edfb09b/swiftenv-install.sh)"