In order to pass a JSON string inside another JSON string in such a scenario, you need to escape it (e.g. manually via JSON Escape/Unescape).
jsonfiddle esc will escape any arbitrary string so as to embed it as content of json string. This seems useless at first, but it actually allows you to embed any arbitrary file into GitHub Gists JSON API, so as to post any arbitrary file onto GitHub Gist:
echo '{"description":"SmartyStreets API Demo","public":true,"files":{"SmartyStreets.json":{"content":'"`jsonfiddle fmt -i test/SmartyStreets.json | jsonfiddle esc -i`"'}}}' | curl --data @- https://api.github.com/gists
This will give you https://gist.github.com/anonymous/1423d4768dd9b88262ca513626e68d8e
By "arbitrary file" I do mean arbitrary file. Check this out:
https://gist.github.com/anonymous/a51798ce99ff59d8d4ba536cbf4b6996
This is why jsonfiddle esc is a command on its own, instead of being part of functionalities of jsonfiddle fmt or jsonfiddle sort.