Update doorkeeper gem (security issue)

Gemfile.lock

@@ -108,7 +108,7 @@ GEM
       thor
     crack (0.4.3)
       safe_yaml (~> 1.0.0)
-    crass (1.0.3)
+    crass (1.0.4)
     daemons (1.2.5)
     dalli (2.7.6)
     debug_inspector (0.0.3)
@@ -122,7 +122,7 @@ GEM
     docile (1.1.5)
     domain_name (0.5.20180417)
       unf (>= 0.0.5, < 1.0.0)
-    doorkeeper (4.2.6)
+    doorkeeper (4.4.0)
       railties (>= 4.2)
     eco (1.0.0)
       coffee-script

db/migrate/20180719033247_add_confidential_to_doorkeeper_application.rb

@@ -0,0 +1,11 @@
+class AddConfidentialToDoorkeeperApplication < ActiveRecord::Migration[5.1]
+  def change
+    add_column(
+      :oauth_applications,
+      :confidential,
+      :boolean,
+      null: false,
+      default: true # maintaining backwards compatibility: require secrets
+    )
+  end
+end