rexml is no longer default

When Rails will be released, we should be able to remove it

Author: benoittgt

example_app_generator/generate_app.rb

@@ -32,6 +32,11 @@
 
   if Rails::VERSION::STRING >= '6'
     gsub_file "Gemfile", /.*rails-controller-testing.*/, "gem 'rails-controller-testing', git: 'https://github.com/rails/rails-controller-testing'"
+
+    # TODO: To remove when Rails released with https://github.com/rails/rails/pull/40281
+    append_to_file 'Gemfile', <<-EOT.gsub(/^ +\|/, '')
+      |gem 'rexml'
+    EOT
   end
 
   if Rails::VERSION::STRING >= '6'