correct use of required annotation in json-schema

https://tools.ietf.org/html/draft-handrews-json-schema-validation-02#section-6.5.3

api/server-server/definitions/keys.yaml

@@ -20,7 +20,6 @@ properties:
   server_name:
     type: string
     description: DNS name of the homeserver.
-    required: true
     example: "example.org"
   verify_keys:
     type: object
@@ -31,7 +30,6 @@ properties:
       algorithm and ``abc123`` being the version in the example below). Together,
       this forms the Key ID. The version must have characters matching the regular
       expression ``[a-zA-Z0-9_]``.
-    required: true
     additionalProperties:
       type: object
       title: Verify Key
@@ -44,8 +42,8 @@ properties:
         key:
           type: string
           description: The `Unpadded Base64`_ encoded key.
-          required: true
           example: "VGhpcyBzaG91bGQgYmUgYSByZWFsIGVkMjU1MTkgcGF5bG9hZA"
+      required: ["key"]
   old_verify_keys:
     type: object
     description: |-
@@ -69,13 +67,12 @@ properties:
           type: integer
           format: int64
           description: POSIX timestamp in milliseconds for when this key expired.
-          required: true
           example: 1532645052628
         key:
           type: string
           description: The `Unpadded Base64`_ encoded key.
-          required: true
           example: "VGhpcyBzaG91bGQgYmUgeW91ciBvbGQga2V5J3MgZWQyNTUxOSBwYXlsb2FkLg"
+      required: ["expired_ts", "key"]
   signatures:
     type: object
     description: Digital signatures for this object signed using the ``verify_keys``.
@@ -103,3 +100,4 @@ properties:
       publishes a key which is valid for a significant amount of time without a way
       for the homeserver owner to revoke it.
     example: 1052262000000
+required: ["server_name", "verify_keys"]