Update get_latest_version algorithms

[spamguy]

Updates get_latest_version algorithms for Redis, Nix, and Electron. They are currently broken.

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

• Updated the versions and releases in the scraper file
• Ensured the license is up-to-date
• 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