Bump flask-migrate from 2.6.0 to 2.7.0 (#180)

Bumps [flask-migrate](https://github.com/miguelgrinberg/flask-migrate) from 2.6.0 to 2.7.0.
- [Release notes](https://github.com/miguelgrinberg/flask-migrate/releases)
- [Changelog](https://github.com/miguelgrinberg/Flask-Migrate/blob/master/CHANGES.md)
- [Commits](https://github.com/miguelgrinberg/flask-migrate/compare/v2.6.0...v2.7.0)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

setup.py

@@ -37,7 +37,7 @@ setup(
     install_requires=[
         'Flask==1.1.2',
         'Flask-SQLAlchemy==2.4.4',
-        'Flask-Migrate==2.6.0',
+        'Flask-Migrate==2.7.0',
         'Flask-Bootstrap==3.3.7.1',
         'Flask-WTF==0.14.3',
         'Flask-Caching==1.10.0',