Flask-Migrate was recently patched to version 1.3.1 because [alembic versions can now include parts that are not integers](https://github.com/miguelgrinberg/Flask-Migrate/pull/51).
Requiring Flask-Migrate 1.3.0 installs a version of alembic that results in the following error message on startup:
`ValueError: invalid literal for int() with base 10: 'post2'`
Changing the requirements to install Flask-Migrate 1.3.1 fixes this problem.