Fix simple typo: differntial -> differential

[timgates42]

Issue Type

[x] Bug (Typo)

Steps to Replicate

1. Examine nba_py/player.py.
2. Search for differntial.

Expected Behaviour

1. Should read differential.

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

To avoid wasting CI processing resources a branch with the fix has been
prepared but a pull request has not yet been created. A pull request fixing
the issue can be prepared from the link below, feel free to create it or
request @timgates42 create the PR.

https://github.com/timgates42/nba_py/pull/new/bugfix_typo_differential

Thanks.