Enhancement: Add filter for $subject in send_notification_email

Hi daymobrew,

Please raise this as an issue over at the plugins github page: https://github.com/l3rady/wp-updates-notifier

You may even create a pull request with your feature if you wish.

Scott

I can probably manage to create a github account and add an issue, but a pull request would be beyond me as I have never used git (I use subversion locally).