There are some legacy/stupid applications[1] that you need to interoperate with, and they for whatever reason require that the JSON you're using is ordered in a particular way (contrary to the JSON specifications).
Unfortunately, the golang authors are not willing to support such a broken use case, so on their advice this is a fork of the golang encoding/json package, with the ordered JSON support originating with a patch from Peter Waldschmidt.
If you can, you should avoid using this package. However, if you can't avoid it, then you are welcome to. Provided under the MIT license, just like golang.