Unsubscribe notifier in ensure block

In case of unhandled exception we should unsubscribe notifier anyway.
Related to #7.

lib/grape_logging/middleware/request_logger.rb

@@ -16,10 +16,15 @@ module GrapeLogging
       def after
         stop_time
         logger.info parameters
-        ActiveSupport::Notifications.unsubscribe(@subscription) if @subscription
         nil
       end
 
+      def call!(env)
+        super
+      ensure
+        ActiveSupport::Notifications.unsubscribe(@subscription) if @subscription
+      end
+
       protected
       def parameters
         {