Fix sessions middleware spec (#1247)

This array structure will work with the new way of loading middleware.

lib/hanami/config/actions/sessions.rb

@@ -62,7 +62,7 @@ module Hanami
         def middleware
           return [] unless enabled?
 
-          [[storage_middleware, options]]
+          [storage_middleware, options].flatten
         end
 
         private

spec/unit/hanami/config/actions/sessions_spec.rb

@@ -42,9 +42,7 @@ RSpec.describe Hanami::Config::Actions, "#sessions" do
     end
 
     it "returns an array of middleware classes and options" do
-      expect(sessions.middleware).to eq [
-        [Rack::Session::Cookie, [secret: "abc"]]
-      ]
+      expect(sessions.middleware).to eq [Rack::Session::Cookie, {secret: "abc"}]
     end
   end
 end