docs: fix Person._name init typo in 05_Object_model/02

[mvanhorn]

Fixes #197

What changed

Notes/05_Object_model/02_Classes_encapsulation.md introduced _name as a private attribute but initialized it to 0:

class Person(object):
    def __init__(self, name):
        self._name = 0

The REPL block directly below then shows:

>>> p = Person('Guido')
>>> p._name
'Guido'

That only works if self._name = name. This PR changes the initializer to match the output shown in the same example.

One-line docs diff.