Fix migration

db/migrate/20190324080634_create_doorkeeper_tables.rb

@@ -18,7 +18,7 @@ def change
 
     create_table :oauth_access_grants do |t|
       t.references :resource_owner,  null: false
-      t.references :application,     null: false, foreign_key: true
+      t.references :application,     null: false
       t.string   :token,             null: false
       t.integer  :expires_in,        null: false
       t.text     :redirect_uri,      null: false
@@ -28,10 +28,15 @@ def change
     end
 
     add_index :oauth_access_grants, :token, unique: true
+    add_foreign_key(
+      :oauth_access_grants,
+      :oauth_applications,
+      column: :application_id
+    )
 
     create_table :oauth_access_tokens do |t|
       t.references :resource_owner, index: true
-      t.references :application,    null: false, foreign_key: true
+      t.references :application,    null: false
 
       # If you use a custom token generator you may need to change this column
       # from string to text, so that it accepts tokens larger than 255
@@ -58,6 +63,11 @@ def change
 
     add_index :oauth_access_tokens, :token, unique: true
     add_index :oauth_access_tokens, :refresh_token, unique: true
+    add_foreign_key(
+      :oauth_access_tokens,
+      :oauth_applications,
+      column: :application_id
+    )
 
     # Uncomment below to ensure a valid reference to the resource owner's table
     add_foreign_key :oauth_access_grants, :users, column: :resource_owner_id