Incorrect logic in release note creation

Hi,

I have used gren for both creating changelog file and generating release notes on the GH releases and have the same wrong results in both cases:

```
# Changelog

## v1.0.7 (29/09/2020)
*No changelog for this release.*

---

## v1.0.6 (29/09/2020)
*No changelog for this release.*

---

## v1.0.5 (29/09/2020)
*No changelog for this release.*

---

## v1.0.4 (29/09/2020)
*No changelog for this release.*

---

## v1.0.3 (29/09/2020)
*No changelog for this release.*

---

## v1.0.2 (29/09/2020)
*No changelog for this release.*

---

## v1.0.1 (29/09/2020)
*No changelog for this release.*

---

## v1.0.0 (29/09/2020)
- List of all the 95 PRs we have.
```

So instead of spreading the 95 PRs in their correct releases, they have all been linked to v1.0.0 (which should just have a few).

I guess this is because the tags/releases have not been created at the time of the commit they are referring to. They have all been created today Sep 29th 2020, but each of them correctly points to the right sha1.

If that is the case, I think that being time-based is not a very robust approach, however it should at least be based on the **date of the commit** the tag is referring to and not the tag's date.

Comece reproduzindo o changelog e a saída do GitHub release descritos na issue, com tags criadas depois de seus commits de destino. Inspecione o ponto de entrada da geração de release notes e como ele determina qual release contém cada pull request. Considera-se concluído quando pull requests históricos são atribuídos usando a data do commit referenciado ou o destino da tag, em vez da data de criação da tag, com cobertura para esse cenário.

Escrita pelo modelo de indexação a partir do texto da issue.