Travis CI: Workaround deployment fail by using dist focal instead

(fix of commits a398d87, a417839)

.travis.yml

@@ -101,6 +101,7 @@ jobs:
       apt:
         packages:
         - libatomic-ops-dev
+    dist: focal
     env:
     - MAKEFILE_TARGETS="distcheck"
     - GC_REAL_VERSION=7.2s
@@ -138,10 +139,6 @@ script:
     gzip --best --verbose gc-*.tar;
   fi
 
-before_deploy:
-- yes | gem update --system --force
-- gem install bundler uri install
-
 deploy:
   provider: releases
   edge: true