Update Rails (from FileScraper to UrlScraper)

[MasterEnoc]

• [x] Updated the versions and releases in the scraper file
• [x] 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
• [x] Ensured the icons and the SOURCE file in public/icons/your_scraper_name/ are up-to-date if the documentation has a custom icon
• [x] Ensured self.links contains up-to-date urls if self.links is defined
• [x] 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

The documentation scraped by the Rails FileScraper did not have source code links but the online documentaciones does. That is the main reason to move Rails from FileScraper to UrlScraper. The source code links would be helpful, as mentioned in #763.