change code format for json fragments to javascript

GitHub is very strict on JSON and interprets ```json``` fenced codeblocks to be JSON documents and highlights colons as errors. You can see an example in the top version below. This is a problem with GitHub IMO but it negatively effects the first developer experience when checking out a library, and so I think it's worth a workaround. Fortunately there's a simple workaround which is to fence JSON fragments with `javascript` and fence only full json documents with `json`. It is still useful to fence full json documents with `json` as you get the error checking.

![testem-readme-shots](https://cloud.githubusercontent.com/assets/4126/2965457/0087ec06-daf7-11e3-85ad-570e597e2e6f.png)