docs: fix OpenAPI Spec example in jest-openapi README (#273)

Author: es80

packages/jest-openapi/README.md

@@ -210,7 +210,8 @@ paths:
           description: Response body should be an ExampleSchemaObject
           content:
             application/json:
-              schema: '#/components/schemas/ExampleSchemaObject'
+              schema: 
+                $ref: '#/components/schemas/ExampleSchemaObject'
 components:
   schemas:
     ExampleSchemaObject: