ini file string value containing value that parses as non-string stringifies without quotes

**Describe the bug**

**Steps to Reproduce**

```
> stringify({ value: "undefined" })
"value=undefined"
> stringify({ value: "1" })
"value=1"
```

**Expected behavior**

These should stringify with quotes like `"undefined"` and `"1"` so that they're not parsed as numbers/undefined/etc.

**Environment**

- OS: [e.g. Ubuntu 20.04, MacOS 11]
- deno version:
- std version: 0.224.0