update Rakefile to use bundler packaging

Author: HamptonMakes

Rakefile

@@ -1,13 +1,7 @@
-require 'rake'
+require 'bundler'
+Bundler::GemHelper.install_tasks
+
 require 'rake/testtask'
-begin
-  # in 1.9
-  require 'rdoc/task'
-rescue LoadError
-  # for 1.8 compat
-  require 'rake/rdoctask'
-end
-require 'rubygems/package_task'
 
 $:.unshift 'lib'
 
@@ -24,20 +18,3 @@ Rake::TestTask.new(:test) do |t|
   t.test_files = Dir.glob("test/**/*_test.rb")
   t.verbose = true
 end
-
-desc 'Generate documentation for the mini_magick plugin.'
-Rake::RDocTask.new(:rdoc) do |rdoc|
-  rdoc.rdoc_dir = 'rdoc'
-  rdoc.title    = 'MiniMagick'
-  rdoc.options << '--line-numbers'
-  rdoc.options << '--inline-source'
-  rdoc.rdoc_files.include('README.rdoc')
-  rdoc.rdoc_files.include('lib/**/*.rb')
-end
-
-spec = eval(File.read('mini_magick.gemspec'))
-Gem::PackageTask.new(spec) do |pkg|
-  pkg.gem_spec = spec
-  pkg.need_zip = true
-  pkg.need_tar = true
-end