Bump sphinx from 1.4.8 to 1.7.6
Bump sphinx from 1.4.8 to 1.7.6

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 1.4.8 to 1.7.6.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v1.4.8...v1.7.6)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
marshmallow-code/marshmallow-sqlalchemy