keep existing formatting in package.json

We will write our own indentation in package.json. For commands that shell out to cordova-fetch and therefore npm, we have no control over it (cordova platform/plugin add/rm).

We could theoretically keep indentaiton for commands where we write to package.json (also platform/plugin add/rm to cordova key & during restore when we sync config.xml & package.json).

This issue is probably not worth implementing.

npm@5 seems like it will respect existing formatting.

Previous issue with npm formatting: https://github.com/npm/npm/issues/5694
npm5 respecting indentation: https://github.com/npm/npm/issues/16244