Update docs/contributing.md

Co-authored-by: Mathieu Kniewallner <mathieu.kniewallner@gmail.com>

Author: neersighted

docs/contributing.md

@@ -245,7 +245,7 @@ Do not forget to `pipx upgrade poetry@master` before using it, to make sure you
 {{% /note %}}
 
 {{% note %}}
-This mechanism can also be used to test pull requests by using Github's pull request remote refs:
+This mechanism can also be used to test pull requests by using GitHub's pull request remote refs:
 ```sh
 pipx install --suffix @pr1234 git+https://github.com/python-poetry/poetry.git@refs/pull/1234/head
 ```