The current logic in `js_to_json` tries to rewrite octal/hex numbers to
decimal. However, when the logic actually happens the `"` or `'` have
already been trimmed off. This causes what were originally strings, that
happen to look like octal/hex numbers, to get rewritten to decimal and
returned as a number rather than a string.

In practive something like:

```js
{
  "0x40": "foo",
  "040": "bar",
}
```

would get rewritten as:

```json
{
  64: "foo",
  32: "bar
}
```

This is problematic since this isn't valid JSON as you cannot have
non-string keys.