Failing test in functions.json :)

Real reason is that we actually want to preserve spaces in the case of a string.  So for example:

```
join(`, `, `["foo", "bar", "baz"]`)
```

Previously the rstrip() would remove the trailing space so the result would be `"foo","bar","baz"` when it should have been `"foo", "bar", "baz"`.   Perhaps I shouldn't even using lstrip() either.  This would mean expressions like `    [0, 1]` would be an error.