Preserve order of keys when possible

[koterpillar]

I'm using git-json-merge to merge package.json files where dependencies are typically sorted alphabetically. It would be useful to have the merge preserve the relative order of items where possible, i.e.:

Base:

{
  "a": 1,
  "c": 3,
  "e": 5
}

Left change:

{
  "a": 1,
  "b": 2,
  "c": 3,
  "e": 5
}

Right change:

{
  "a": 1,
  "c": 3,
  "d": 4,
  "e": 5
}

Expected output:

{
  "a": 1,
  "b": 2,
  "c": 3,
  "d": 4,
  "e": 5
}

Actual output:

{
  "a": 1,
  "c": 3,
  "e": 5,
  "d": 4,
  "b": 2
}