Don't inject on text/json Content-type pages

Great extension, first of all.

Love the work.

Now, whenever I copy a js/json/text file from Git or wherever, the injected elements get copied as well.

Specifically,

Viewport
Window
×
×
×

So, for example, if I copy jquery's source and paste it in one of my projects, I always copy this with it, thereby, breaking the code.

Thought I would bring it to your attention.

Thanks,