MultiJson.encode is deprecated and gives warnings.
update MultiJson.encode to MultiJson.dump
MultiJson.encode is deprecated.
this requires multi_json ~> 1.3.0, which I added to the gemspec.
Otherwise, I would recommend updating the gemspec to set multi_json to "~> 1.2.0" so as not to break the library when multi_json 1.4.0 comes out and deprecates the methods used, as "~> 1.2" will match "1.4".
I'm not changing the gemspec from "~> 1.0". That needs to stay until sprockets 2.0.
We're going to have to feature detect the new api.