fix the issue for updated notification or show new notification if creat...

Thank you for creating this plugin. I have tried using it and found one bug. When I created a notification it was created successfully. But it seems that earlier code for comparing time was not working for me. So I have changed to now(). 

Following is the scenario I have tried :
-> Created notification
-> hide if from browser
-> created another notification
-> It is expected to see in browser as its new for my user, but its not because we have set flag in session which prevents showing new notification.

So I have changed the logic with hide_time which will be useful to check based on updated_at.