Update flask-migrate to 2.4.0

[pyup-bot]

This PR updates Flask-Migrate from 2.0.1 to 2.4.0.

Changelog

2.4.0

- Refreshed the env.py files from the Alembic project (216)

2.3.1

- Don't silence transaction errors from SQLAlchemy (236)

2.3.0

- Use root logger for alembic error messages
- Add `--indicate-current` option to history command (192)

2.2.1

- Drop support for Alembic versions before 0.7
- Added pypy3 to test matrix

2.2.0

- Suppress stack traces on command errors (204)

2.1.1

- Make the `directory` argument to `get_config()` optional (168)

2.1.0

- Removed dependency on Flask-Script from setup.py (165)

2.0.4

- Support -x arguments in "migrate" command (148)

2.0.3

- Support multiple -x arguments in the Flask-Script interface (103)

2.0.2

- Support passing alembic context kwargs from constructor into init_app (138)

Links

• PyPI: https://pypi.org/project/flask-migrate
• Changelog: https://pyup.io/changelogs/flask-migrate/
• Repo: http://github.com/miguelgrinberg/flask-migrate/
• Docs: https://pythonhosted.org/Flask-Migrate/