Bug: Superfluous comma in flow style

Version: `latest`

To reproduce:

`printf "---\n- {foo: bar}\n\n" | yamlfmt -formatter "include_document_start=true" -formatter "retain_line_breaks=true" -`

Actual Input:
```yaml
---
- {foo: bar}

```

Actual Output:
```yaml
---
- {foo: bar,}

```

Expected Output:
```yaml
---
- {foo: bar}

```

---

Also note that the following works fine:

`printf "---\n- {foo: bar}\n" | yamlfmt -formatter "include_document_start=true" -formatter "retain_line_breaks=true" -`

Thanks for your work on this!