Parsing broken with apostrophe in quoted parameter of cell metadata

[matthew-brett]

I just noticed that the notebooks like the following:

---
jupyter:
  jupytext:
    notebook_metadata_filter: all,-language_info
    split_at_heading: true
    text_representation:
      extension: .Rmd
      format_name: rmarkdown
      format_version: '1.2'
      jupytext_version: 1.14.6
---
```{python some-name, param="Problem's"}
a = 1
```

This gives the following error when trying to load the notebook:

[W 17:33:09.623 NotebookApp] Option line "some-name, param="Problem's"" is not properly terminated

Removing the apostrophe fixes the error:

```{python some-name, param="Problems"}
```

[mwouts]

Hey @matthew-brett , thank you for reporting this. I will see what I can do.

[matthew-brett]

Great - thank you!