Obey bundler convensions in gemspec, Gemfile, and Rakefile

Gemfile

@@ -1,3 +1,2 @@
-source "http://rubygems.org"
-
+source :rubygems
 gemspec

Rakefile

@@ -1,15 +1,9 @@
 require 'rubygems'
 require 'bundler/setup'
-require 'rake/gempackagetask'
+require "bundler/gem_tasks"
 require 'rspec/core/rake_task'
 require 'cucumber/rake/task'
 
-eval("$specification = #{IO.read('appraisal.gemspec')}")
-Rake::GemPackageTask.new($specification) do |package|
-  package.need_zip = true
-  package.need_tar = true
-end
-
 RSpec::Core::RakeTask.new do |t|
   t.pattern = 'spec/**/*_spec.rb'
 end