Fix 'Passing strings or symbols to the middleware builder' Rails 5 deprecation warning

Author: nihtalak

lib/detectify/railtie.rb

@@ -1,7 +1,7 @@
 module Detectify
   class Railtie < Rails::Railtie
     initializer 'detectify' do |app|
-      app.config.middleware.use 'Detectify::Middleware'
+      app.config.middleware.use Detectify::Middleware
     end
   end
 end