Configure the plugin so we can use it to format JSON

[remileduc]

clang-format can work with JSON, but it seems the plugin doesn't alllow it.

Indeed, if I set the following in the settings.json:

"[json]": {
    "editor.defaultFormatter": "xaver.clang-format"
}

I have the following error:

I think this is related to #146 as it seems to just be a configuration issue

Edit: it seems it has already be done by #139, but no update in marketplace like described in #113

Edit 2: For those who wants to have it working, you can install the fork https://github.com/seaube/vscode-clang-format instead