Move hidden attribute from group to team.

Author: eldering

contest-api/json-schema/group.json

@@ -8,8 +8,7 @@
 		"id": { "$ref": "common.json#/identifier" },
 		"icpc_id": { "type": [ "string", "null" ] },
 		"name": { "type": "string" },
-		"type": { "type": "string" },
-		"hidden": { "type": "boolean" }
+		"type": { "type": "string" }
 	},
 	"required": ["id", "name"],
 	"$ref": "common.json#/strictproperties"

contest-api/json-schema/team.json

@@ -15,6 +15,7 @@
 			"uniqueItems": true,
 			"items": { "$ref": "common.json#/identifierornull" }
 		},
+		"hidden": { "type": [ "boolean", "null" ] },
 		"location": {
 			"type": "object",
 			"properties": {