Duplicate keys lost

[bmish]

Values for duplicate object keys as seen in simulated package.json comments are lost when editing a file.

Before editing package.json:

{
  "dependencies": {
    "//": "comment about foo",
    "foo": "^1.2.3",
    "//": "comment about bar",
    "bar": "^4.5.6",
    "//": "comment about baz",
    "baz": "^7.8.9",
  }
}

After some arbitrary edit to package.json:

{
  "dependencies": {
    "//": "comment about baz",
    "foo": "^1.2.3",
    "bar": "^4.5.6",
    "baz": "^7.8.9",
  }
}

While I don't expect to be able to edit the duplicate keys as there's no way to refer to them individually, I do need to be able to edit other data in the file without losing the comments.

Note that this is different from #40 which is referring to actual comments, not the simulated comments involved here.

This bug causes me a problem in my tool in bmish/check-dependency-version-consistency#536.