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

@@ -7,7 +7,7 @@ source script/functions.sh
 
 if is_ruby_23_plus; then
   gem update --system
-  gem install bundler
+  gem install bundler --conservative
 else
   echo "Warning installing older versions of Rubygems / Bundler"
   gem update --system '2.7.8'