version Gemfile.lock; call Bundler.setup() in Rakefile

Rakefile

@@ -1,3 +1,9 @@
+require "bundler"
+begin
+  Bundler.setup(:default, :development)
+rescue Bundler::BundlerError => e
+  raise LoadError.new("Unable to setup Bundler; you might need to `bundle install`: #{e.message}")
+end
 require "bundler/gem_tasks"
 require 'rspec/core/rake_task'
 require "rdoc/task"