Remove bundler setup from Rakefile

Rakefile

@@ -1,20 +1,6 @@
 # encoding: utf-8
 
-require 'rubygems'
-require 'bundler'
 require 'bundler/gem_tasks'
-
-begin
-  Bundler.setup(:default, :development)
-rescue Bundler::BundlerError => e
-  $stderr.puts e.message
-  $stderr.puts "Run `bundle install` to install missing gems"
-  exit e.status_code
-end
-
-require 'rake'
-
-require 'rspec/core'
 require 'rspec/core/rake_task'
 RSpec::Core::RakeTask.new(:spec) do |spec|
   spec.pattern = FileList['spec/**/*_spec.rb']