Downgrade to older bundler on older rails

.travis.yml

@@ -24,6 +24,7 @@ bundler_args: "--binstubs --path ../bundle --retry=3 --jobs=3"
 
 before_install:
   - script/update_rubygems_and_install_bundler
+  - script/downgrade_bundler_on_old_rails
   - script/clone_all_rspec_repos
 
 before_script:

script/downgrade_bundler_on_old_rails

@@ -0,0 +1,19 @@
+#!/bin/bash
+# This file was generated on 2019-01-03T20:34:23+00:00 from the rspec-dev repo.
+# DO NOT modify it by hand as your changes will get lost the next time it is generated.
+
+set -e
+source script/functions.sh
+
+if ruby -e "exit(ENV['RAILS_VERSION'].to_f < 5)"; then
+  # On Rails versions less than 5, Bundler 2.0 is not supported
+  echo "Warning dowgrading to older version of Bundler"
+  gem uninstall -aIx bundler
+
+  # this only works on Ruby 2.3 which is luckily the version we need to fix
+  if is_ruby_23_plus; then
+    rvm @global do gem uninstall -aIx bundler
+  fi
+
+  gem install bundler -v '1.17.3'
+fi