* Remove spread operator
I believe what was meant here was to express that you would create the new player object with all the previous properties of the existing player object in addition to now updating the score value. That being said, this is a simple example, and the player object clearly has no other values. Objects are not (by default) iterable using this operator, so this little piece does more harm than good. I believe the new example to be much clearer.
* Using Object.assign()
* Tweak wording
The tutorial wants to throw a 'warning' and explains about 'key' of React's list, but it throws nothing since there is sensible key.
"key={move}" should be removed, and added after explaining about key.
