Check for bundler

Rakefile

begin
  require 'bundler'
  Bundler.setup(:default, :development)
rescue Bundler::BundlerError => e
  $stderr.puts e.message
  $stderr.puts "Run `bundle install` to install dependencies"
  exit e.status_code
rescue Gem::LoadError => e
  $stderr.puts e.message
  $stderr.puts "Run `gem install bundle` to install bundler"
  $stderr.puts "Then, run `bundle install` to install dependencies" 
  exit e.status_code
end