Merge branch 'rs-update-unicorn' into 'master'

Bump unicorn to `~> 4.9.0`

Closes #2820 

See merge request !2843

Gemfile

@@ -112,7 +112,7 @@ gem 'diffy', '~> 3.0.3'
 
 # Application server
 group :unicorn do
-  gem "unicorn", '~> 4.8.2'
+  gem "unicorn", '~> 4.9.0'
   gem 'unicorn-worker-killer', '~> 0.4.2'
 end
 

Gemfile.lock

@@ -833,7 +833,7 @@ GEM
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.7.1)
-    unicorn (4.8.3)
+    unicorn (4.9.0)
       kgio (~> 2.6)
       rack
       raindrops (~> 0.7)
@@ -1034,7 +1034,7 @@ DEPENDENCIES
   uglifier (~> 2.7.2)
   underscore-rails (~> 1.8.0)
   unf (~> 0.1.4)
-  unicorn (~> 4.8.2)
+  unicorn (~> 4.9.0)
   unicorn-worker-killer (~> 0.4.2)
   version_sorter (~> 2.0.0)
   virtus (~> 1.0.1)