update() method will replace a JSON document in a dataset collection
for a given KEY.
Let’s assume our JSON document contains {"name":"Jane Doe"} and the
KEY is “jane.doe” and our collection name is “people.ds”.
c_name = "people.ds"
key = "jane.doe"
obj = {"name":"Jane Doiel"}
if not dataset.update(c_name, key_obj):
print(dataset.error_message()
The update() method returns True on success or False otherwise.