[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

CONTRIBUTING.md

@@ -79,7 +79,7 @@ We want your work to be readable by others; therefore, we encourage you to note
   [black](https://github.com/psf/black),
   [isort](https://github.com/PyCQA/isort),
   [mypy](http://mypy-lang.org) and
-  [flake8](https://flake8.pycqa.org/en/latest/). 
+  [flake8](https://flake8.pycqa.org/en/latest/).
 
 - Original code submission require docstrings or comments to describe your work.
 
@@ -141,7 +141,7 @@ We want your work to be readable by others; therefore, we encourage you to note
   starting_value = int(input("Please enter a starting value: ").strip())
   ```
 
-  The use of [Python type hints](https://docs.python.org/3/library/typing.html) is encouraged for function parameters and return values. 
+  The use of [Python type hints](https://docs.python.org/3/library/typing.html) is encouraged for function parameters and return values.
   Our automated testing will run [mypy](http://mypy-lang.org) so run that locally with pre-commit before making your submission.
 
   ```python