XDownloadOptions spec referenced wrong class

Author: stve

spec/lib/secure_headers/headers/x_download_options_spec.rb

@@ -24,7 +24,7 @@ module SecureHeaders
 
       it "doesn't accept anything besides noopen" do
         expect {
-          XContentTypeOptions.new("open")
+          XDownloadOptions.new("open")
         }.to raise_error
       end
     end