Add rdoc and rake to gemspec dev dependencies

Author: sshao

libxslt-ruby.gemspec

@@ -36,6 +36,8 @@ Gem::Specification.new do |spec|
                          'ext/vc/*.vcxproj',
                          'test/**/*'])
   spec.test_files = Dir.glob("test/test_*.rb")
+  spec.add_development_dependency 'rdoc'
+  spec.add_development_dependency 'rake'
   spec.add_development_dependency 'rake-compiler'
   spec.required_ruby_version = '>= 1.8.7'
   spec.date = DateTime.now