switch to Ruby

See #59, release log:

• fb9be4f by @yegor256: #59 karma
• ff1ca24 by @yegor256: #59 check fixed
• 62e1d5f by @yegor256: #59 update bundler
• cd768d2 by @yegor256: #59 rultor image
• 4a471b0 by @yegor256: #59 heroku
• 85f49e0 by @yegor256: #59 udpate
• 54bf3e8 by @yegor256: #59 deps
• f87db80 by @yegor256: #59 authors
• 47e5a2c by @yegor256: #59 script
• f5ca9c9 by @yegor256: #59 /recent
• 7b9b5db by @yegor256: #59 /recent
• 83f4263 by @yegor256: #59 logos
• 42bcc23 by @yegor256: #59 switch to Ruby

Released by Rultor 1.68.9, see build log