Ch4: remove jsonify from examples

[adrienbrunet]

Hi There, this book is absolutely marvellous and I haven't read half of it yet. Thanks a ton!!

In Chapter 4 and maybe elsewhere, jsonify is used in the flask views to return the response.
Since flask 1.1, (see changelog), it is not mandatory.

Allow returning a dictionary from a view function. Similar to how returning a string will produce a text/html response, returning a dict will call jsonify to produce a application/json response. #3111

Since this book is not on flask itself, it may give an even simpler code example. If you think it makes the reader more aware of the nature of the response, I totally understand and this issue can be closed.

Thanks again ! All the best