Modify JSON Patch example

Rules for the patch keyword would be:

* must be an object,
* must have "source" and "with" members,
* "source" must be a valid JSON Schema,
* "with" must be a JSON Patch,
* must not be used in combination with $ref,
* other members (keyword or not) should be ignored.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>