fix "uninitialized constant Gem::UserInteraction" error in webui

On older version of rubygems, I get the following error when trying to visit the geminabox web ui:
uninitialized constant Gem::UserInteraction
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb	16	in `'
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb	14	in `'
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb	36	in `require'
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb	36	in `require'
/usr/local/rvm/gems/ruby-1.9.3-p125/gems/geminabox-0.11.0/lib/geminabox.rb	5	in `'
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb	60	in `require'
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb	60	in `rescue in require'
/usr/local/rvm/rubies/ruby-1.9.3-p125/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb	35	in `require'
config.ru	2	in `block in
/usr/local/rvm/gems/ruby-1.9.3-p125/gems/rack-1.5.2/lib/rack/builder.rb	55	in `instance_eval'
/usr/local/rvm/gems/ruby-1.9.3-p125/gems/rack-1.5.2/lib/rack/builder.rb	55	in `initialize'
config.ru	1	in `new'
config.ru	1	in `
/usr/local/rvm/gems/ruby-1.9.3-p125/gems/passenger-3.0.11/lib/phusion_passenger/rack/application_spawner.rb	225	in `eval'

This problem occurs on several versions of rubygems that I tested: 1.8.19 and 1.8.25, but does not occur on 2.0.7.  The attached fix makes it works in all versions now.