docs: Fix a few typos

[timgates42]

There are small typos in:

• docs/examples.rst
• leather/utils.py

Fixes:

• Should read overridden rather than overriden.
• Should read implementation rather than implemenation.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

[jpmckinney]

Thanks!