libruby2.7 has rexml 3.2.3.1 which has latest security fixes

--- a/Gemfile
+++ b/Gemfile
@@ -51,7 +51,7 @@
 gem 'bcrypt', '~> 3.1', '>= 3.1.14'
 gem 'doorkeeper', '~> 5.5'
 gem 'doorkeeper-openid_connect', '~> 1.8'
-gem 'rexml', '~> 3.2', '>= 3.2.5'
+gem 'rexml', '~> 3.2', '>= 3.2.3.1'
 gem 'ruby-saml', '~> 1.13'
 gem 'omniauth', '~> 2.1'
 gem 'omniauth-auth0', '~> 2.0'