Unify category format in frontmatter

[satotake]

Related #4
Very tiny PR.

Background

I wondered if category' s value (such as Reference or Add-ons) in frontmatter should be translated.
I found that members had also mentioned in #21 .
But it remains unclear if they should be translated or not.
I studied how they are used in this repo.

Conclusion

The values of category are not used anywhere in reactjs.org at least for now.
Therefore, whichever is ok currently.
It will be better not to translate them and leave them as they are, considering they might be used for unknown purposes in the future.

I checked

• no strings of category in public dir after building sites
• no GraphQL query containing category
• Node type in src/types.js does not have category
• In gatsby dir, only redirect_from and permalink are used as frontmatter value
• Backend seach engine is docsearch, which use only html files as data source

[smikitky]

Thank you, this should have been mentioned in the TRANSLATION.md. Many *.md files lack this field in the first place, so I also think this is an unimportant field for now.

[koba04]

👍

[koba04]

@satotake mergeしました！ありがとうございます！ 🚀🚀