Allows emacs version to parse json

Fixes issue: https://github.com/igrigorik/vimgolf/issues/132
yeah. this is weird. what happens if you just leave it out? i'm wondering because it looks like you're just referencing a free variable down on line 305 which is set in the `url-http.el` code. You shouldn't need to declare it to use it, we'll just get a warning.

If I have some free time I'll try to dig into this too.