http://laravel.com/docs/5.1/validation#rule-unique
Forcing A Unique Rule To Ignore A Given ID:
Sometimes, you may wish to ignore a given ID during the unique check. For example, consider an "update profile" screen that includes the user's name, e-mail address, and location. Of course, you will want to verify that the e-mail address is unique. However, if the user only changes the name field and not the e-mail field, you do not want a validation error to be thrown because the user is already the owner of the e-mail address. You only want to throw a validation error if the user provides an e-mail address that is already used by a different user. To tell the unique rule to ignore the user's ID, you may pass the ID as the third parameter:
'email' => 'unique:users,email_address,'.$user->id