PyUp Update sphinx-exec-code to 0.8

[pyup-bot]

This PR updates sphinx-exec-code from 0.6 to 0.8.

Changelog

### 0.7 ``` - Added config parameter to specify stdout encoding - Only empty lines of the output get trimmed ```

Links

- PyPI: https://pypi.org/project/sphinx-exec-code - Changelog: https://pyup.io/changelogs/sphinx-exec-code/ - Repo: https://github.com/spacemanspiff2007/sphinx-exec-code