`bundle update`

I don't know how this is generally handled, but I figured I'd try it anyway. This MR updates all the gems that have newer versions within the Gemfile's restrictions.

All tests passing, GitLab works just fine locally. Only problem I ran into was Sprockets-Rails 3.x breaking Teaspoon, which I fixed by limiting it to 2.x versions. There were a handful of significant version bumps, but mostly just minor/patch-level version bumps.

Changelogs for minor and/or major updates:

• Bullet, 4.14.10 => v5.0.0
• Flay, 2.6.1 => 2.7.0
• rqrcode, 0.7.0 => 0.10.1
• web-console, 2.2.1 => 2.3.0
• Sidekiq, 4.0.1 => 4.1.1
• benchmark-ips, 2.3.0 => 2.5.0