server: fix crash when Fixnum is sent as a message

lib/tork/server.rb:45:in `block (2 levels) in loop':
undefined method `empty?' for 6:Fixnum (NoMethodError)
add bundler configuration helper: bundle in master

This lets you run Tork in an application that uses Bundler without
having to first add Tork to its Gemfile and then bundle install it.