Update Unicorn and associated gems

Unicorn 5.3.1 fixes a GC issue that causes a crash, and Unicorn 5.4.1
quiets some warnings for Ruby 2.6. More details:

https://github.com/defunkt/unicorn/releases

Gemfile

@@ -143,7 +143,7 @@ gem 'diffy', '~> 3.1.0'
 gem 'rack', '2.0.6'
 
 group :unicorn do
-  gem 'unicorn', '~> 5.1.0'
+  gem 'unicorn', '~> 5.4.1'
   gem 'unicorn-worker-killer', '~> 0.4.4'
 end
 

Gemfile.lock

@@ -422,7 +422,7 @@ GEM
       activerecord
       kaminari-core (= 1.0.1)
     kaminari-core (1.0.1)
-    kgio (2.10.0)
+    kgio (2.11.2)
     knapsack (1.17.0)
       rake
     kubeclient (4.2.2)
@@ -666,7 +666,7 @@ GEM
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
     rainbow (3.0.0)
-    raindrops (0.18.0)
+    raindrops (0.19.0)
     rake (12.3.2)
     rb-fsevent (0.10.2)
     rb-inotify (0.9.10)
@@ -898,7 +898,7 @@ GEM
       unf_ext
     unf_ext (0.0.7.5)
     unicode-display_width (1.3.2)
-    unicorn (5.1.0)
+    unicorn (5.4.1)
       kgio (~> 2.6)
       raindrops (~> 0.7)
     unicorn-worker-killer (0.4.4)
@@ -1169,7 +1169,7 @@ DEPENDENCIES
   u2f (~> 0.2.1)
   uglifier (~> 2.7.2)
   unf (~> 0.1.4)
-  unicorn (~> 5.1.0)
+  unicorn (~> 5.4.1)
   unicorn-worker-killer (~> 0.4.4)
   validates_hostname (~> 1.0.6)
   version_sorter (~> 2.1.0)