Bump flask-migrate from 2.5.1 to 2.5.2 in /{{cookiecutter.app_name}}

Bumps [flask-migrate](https://github.com/miguelgrinberg/flask-migrate) from 2.5.1 to 2.5.2.
- [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/v2.5.1...v2.5.2)

{{cookiecutter.app_name}}/Pipfile

@@ -18,7 +18,7 @@ psycopg2 = "==2.8.2"
 SQLAlchemy = "==1.3.3"
 
 # Migrations
-Flask-Migrate = "==2.5.1"
+Flask-Migrate = "==2.5.2"
 
 # Forms
 Flask-WTF = "==0.14.2"