react: update to 16.12.0

[simon04]

If you're updating an existing documentation to it's latest version, please ensure that you have:

• Updated the versions and releases in the scraper file
• Ensured the license is up-to-date and that the documentation's entry in the array in about_tmpl.coffee matches it's data in self.attribution
• Ensured the icons and the SOURCE file in public/icons/your_scraper_name/ are up-to-date if the documentation has a custom icon
• Ensured self.links contains up-to-date urls if self.links is defined
• Tested the changes locally to ensure:
  • The scraper still works without errors
  • The scraped documentation still looks consistent with the rest of DevDocs
  • The categorization of entries is still good

Ad license: https://reactjs.org/docs/getting-started.html and https://github.com/reactjs/reactjs.org/blob/master/src/theme.js and facebook/react#13593 mention different licenses. Let's stick with the current one?

[j-f1]

Fixes in 038869a