Bump sidekiq from 5.2.9 to 6.1.2

Bumps [sidekiq](https://github.com/mperham/sidekiq) from 5.2.9 to 6.1.2.
- [Release notes](https://github.com/mperham/sidekiq/releases)
- [Changelog](https://github.com/mperham/sidekiq/blob/master/Changes.md)
- [Commits](sidekiq/sidekiq@v5.2.9...v6.1.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Gemfile.lock

@@ -378,8 +378,6 @@ GEM
     rack-openid (1.4.2)
       rack (>= 1.1.0)
       ruby-openid (>= 2.1.8)
-    rack-protection (2.0.8.1)
-      rack
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (5.2.3)
@@ -425,7 +423,7 @@ GEM
     rdiscount (2.2.0.2)
     recaptcha (4.14.0)
       json
-    redis (4.1.4)
+    redis (4.2.2)
     ref (2.0.0)
     regexp_parser (1.7.1)
     representable (3.0.4)
@@ -494,11 +492,10 @@ GEM
       rubyzip (>= 1.2.2)
     sentry-raven (3.1.0)
       faraday (>= 1.0)
-    sidekiq (5.2.9)
-      connection_pool (~> 2.2, >= 2.2.2)
+    sidekiq (6.1.2)
+      connection_pool (>= 2.2.2)
       rack (~> 2.0)
-      rack-protection (>= 1.5.0)
-      redis (>= 3.3.5, < 4.2)
+      redis (>= 4.2.0)
     signet (0.14.0)
       addressable (~> 2.3)
       faraday (>= 0.17.3, < 2.0)