Do not install bundler if it is already there

Bundler is installed along with latest versions of `rubygems-update`

Author: pirj

script/update_rubygems_and_install_bundler

@@ -6,8 +6,8 @@ set -e
 source script/functions.sh
 
 if is_ruby_23_plus; then
+  gem install bundler --conservative
   gem update --system
-  gem install bundler
 else
   echo "Warning installing older versions of Rubygems / Bundler"
   gem update --system '2.7.8'