Add AS2 context to Example 60

Per issue #441, example 60 is missing its AS2 context. This change adds an erratum to correct this mistake. Once accepted, we can also merge to the editor's version of the spec itself.

Author: evanp

ERRATA.md

@@ -79,6 +79,33 @@ This document includes errata for the [Activity Streams](https://www.w3.org/TR/a
 
   - Unlike `latitude` and `longitude`, the domain of the `altitude` term is the `Object` type. The `altitude` term should be included in the list of properties of an `Object`. Because `altitude` is primarily documented as a property of a `Place`, publishers should not include `altitude` on objects that are not of type `Place`, and consumers should accept objects with this property that aren't of type `Place`.
 
+  - Example 60, for the `Tombstone` type, is missing the `@context` property. The correct example should be:
+
+    ```json
+    {
+      "@context": "https://www.w3.org/ns/activitystreams",
+      "type": "OrderedCollection",
+      "totalItems": 3,
+      "name": "Vacation photos 2016",
+      "orderedItems": [
+        {
+          "type": "Image",
+          "id": "http://image.example/1"
+        },
+        {
+          "type": "Tombstone",
+          "formerType": "Image",
+          "id": "http://image.example/2",
+          "deleted": "2016-03-17T00:00:00Z"
+        },
+        {
+          "type": "Image",
+          "id": "http://image.example/3"
+        }
+      ]
+    }
+    ```
+
   - The domain of the `attributedTo` property is both `Link` and `Object`. `attributedTo` should be included in the list of properties of a `Link`.
 
   - Example 102 is missing a `type` property on the `Link` value of the `url` property. For clarity, the example should read: