Downgrade Sidekiq to 2.15.1 because our sidekiq workers are dying

Gemfile

@@ -108,7 +108,7 @@ gem 'rest-client'
 gem 'rinku'
 gem 'sanitize'
 gem 'sass'
-gem 'sidekiq'
+gem 'sidekiq', '2.15.1'
 gem 'sidekiq-failures'
 gem 'sinatra', require: nil
 gem 'slim'  # required for sidekiq-web

Gemfile_rails4.lock

@@ -345,8 +345,8 @@ GEM
     redis-activesupport (4.0.0)
       activesupport (~> 4)
       redis-store (~> 1.1.0)
-    redis-namespace (1.3.1)
-      redis (~> 3.0.0)
+    redis-namespace (1.3.2)
+      redis (~> 3.0.4)
     redis-rack (1.5.0)
       rack (~> 1.5)
       redis-store (~> 1.1.0)
@@ -389,8 +389,8 @@ GEM
     shoulda-context (1.1.5)
     shoulda-matchers (2.4.0)
       activesupport (>= 3.0.0)
-    sidekiq (2.15.2)
-      celluloid (>= 0.15.2)
+    sidekiq (2.15.1)
+      celluloid (>= 0.15.1)
       connection_pool (>= 1.0.0)
       json
       redis (>= 3.0.4)
@@ -528,7 +528,7 @@ DEPENDENCIES
   sass-rails
   seed-fu!
   shoulda
-  sidekiq
+  sidekiq (= 2.15.1)
   sidekiq-failures
   sidetiq (>= 0.3.6)
   simple_handlebars_rails!