ci: Hack around a Travis condition, I guess

.travis.yml

@@ -47,6 +47,10 @@ install:
   - bundle install --path=vendor/bundle --with pam_authentication --without development production --retry=3 --jobs=16
   - yarn install
 
+# https://github.com/travis-ci/travis-ci/issues/9333
+before_install:
+  - gem install bundler
+
 before_script:
   - travis_wait ./bin/rails parallel:create parallel:load_schema parallel:prepare assets:precompile