Update flask_migrate to 2.5.2

[pyup-bot]

This PR updates flask_migrate from 2.3.1 to 2.5.2.

Changelog

2.5.2

- add python 3.7 builds, remove 3.4 ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/1af28ba273de6c88544623b8dc02dd539340294b))
- auto-generate change log during release ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/250a3110ad84ba331ffc7cb871e5a12fddc55f2d))
- Nicer change log ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/829edefe09dff82b6c91203dd0f5b5795bf9c8d1))

2.5.1

- Fix `__version__` file not found in sdist [267](https://github.com/miguelgrinberg/flask-migrate/issues/267) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/8ba8d7dca6cb233280d4644fc8d81cbba123a5ad)) (thanks **Christoph Gohlke**!)

2.5.0

- helper release script ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/fb041b9b9221e7125e5ee27dd9eb7514cf143181))
- support % character in database URLs [59](https://github.com/miguelgrinberg/flask-migrate/issues/59) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/4663819b416dfb5a450fe948e84111af3712078d))
- log command output in unit tests ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/506f3541c04dd0b2c020dbafc60a93fb541ca324))
- add a section on why use this extension to the docs [101](https://github.com/miguelgrinberg/flask-migrate/issues/101) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/5467b295f7912d195333482325052eae81d30f7a))

2.4.0

- updates to env.py ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/2a1ae1b9aa62c246fca2b2f1566284de8d4b940b))
- Link to binds is unreachable [244](https://github.com/miguelgrinberg/flask-migrate/issues/244) The original link redirects to flask-sqlalchemy.pocoo.org Addressing it directly works and redirects to the latest version of flask-sqlalchemy ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/eb2ab8f797a179d807b6560947f4498bb543def0)) (thanks **FaBrand**!)

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/