Merge branch 'upgrade-sidekiq' into 'master'

Upgrade Sidekiq from 4.1.2 to 4.1.4.

Adds a dependency on Sinatra and allows Sinatra 2 for eventual support of Rack 2.

Changelog: https://github.com/mperham/sidekiq/blob/master/Changes.md#414

Working toward #14286. 

See merge request !5044

Gemfile.lock

@@ -660,10 +660,11 @@ GEM
       rack
     shoulda-matchers (2.8.0)
       activesupport (>= 3.0.0)
-    sidekiq (4.1.2)
+    sidekiq (4.1.4)
       concurrent-ruby (~> 1.0)
       connection_pool (~> 2.2, >= 2.2.0)
       redis (~> 3.2, >= 3.2.1)
+      sinatra (>= 1.4.7)
     sidekiq-cron (0.4.0)
       redis-namespace (>= 1.5.2)
       rufus-scheduler (>= 2.0.24)
@@ -674,8 +675,8 @@ GEM
       json (~> 1.8)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
-    sinatra (1.4.6)
-      rack (~> 1.4)
+    sinatra (1.4.7)
+      rack (~> 1.5)
       rack-protection (~> 1.4)
       tilt (>= 1.3, < 3)
     six (0.2.0)