Updated README.md for notification type (#99)

Added "type" to the "Props" list cause it was missing.

README.md

@@ -72,6 +72,7 @@ All props are optional.
 | Name           | Type    | Default      | Description |
 | ---           | ---     | ---          | ---         |
 | group          | String  | null         | Name of the notification holder, if specified |
+| type           | String  | null         | Class that will be assigned to the notification |
 | width          | Number/String  | 300          | Width of notification holder, can be `%`, `px` string or number.<br>Valid values: '100%', '200px', 200 |
 | classes        | String/Array | 'vue-notification' | List of classes that will be applied to notification element |
 | position       | String/Array | 'top right'  | Part of the screen where notifications will pop out |