Some fixes

Hi there,

i ran into problems using your gem today, tried to fix them and am now humbly presenting the changes :)

Changed the cdn-url, because browsers nowadays refuse to execute scripts from raw.github.com (see https://github.com/blog/1482-heads-up-nosniff-header-support-coming-to-chrome-and-firefox).
cloudfare was the first one google spat out.

Had to change ```request``` to ```feature``` in order to be able to run the specs.

And regarding the changes in #call inside rack.rb:
I'm not entirely sure of the why and how, but it seems to work.
Before, it didn't render the page-under-test at all, but instead the content of ```@status, @headers, @body```

Cheers