Update rake tasks to use rspec 2.

Rakefile

@@ -8,16 +8,9 @@ end
 
 task :default => [:test, :spec]
 
-begin
+require 'rspec/core/rake_task'
-  require 'spec/rake/spectask'
+desc "Run specs"
-
+RSpec::Core::RakeTask.new
-  desc "Run specs"
-  Spec::Rake::SpecTask.new(:spec) do |t|
-    t.spec_files = FileList["spec/**/*.rb"]
-  end
-rescue LoadError
-  puts "Spec task can't be loaded. `gem install rspec`"
-end
 
 begin
   require 'jeweler'