v2.10.0

• fix typo (@wonda-tea-coffee) #504
• Switch to Rouge for syntax highlighting and add dark syntax-highlighting theme (@RobinDaugherty) #500
• Syntax highlighter uses classes, style-src locked down (@RobinDaugherty) #499
• Use SASS to build CSS (@RobinDaugherty) #498
• Add Content Security Policy (@RobinDaugherty) #497
• Add Rails 6.1 to CI matrix (@RobinDaugherty) #493