Update flask-sqlalchemy to 2.2

[pyup-bot]

There's a new version of Flask-SQLAlchemy available.
You are currently using 2.1. I have updated it to 2.2

These links might come in handy: PyPI | Changelog | Repo | Docs

Changelog

2.2

---

Released on February 27, 2017, codename Dubnium

• Minimum SQLAlchemy version is 0.8 due to use of sqlalchemy.inspect.
• Added support for custom query_class and model_class as args
  to the SQLAlchemy constructor. (328_)
• Allow listening to SQLAlchemy events on db.session. (364_)
• Allow __bind_key__ on abstract models. (373_)
• Allow SQLALCHEMY_ECHO to be a string. (409_)
• Warn when SQLALCHEMY_DATABASE_URI is not set. (443_)
• Don't let pagination generate invalid page numbers. (460_)
• Drop support of Flask < 0.10. This means the db session is always tied to
  the app context and its teardown event. (461_)
• Tablename generation logic no longer accesses class properties unless they
  are declared_attr. (467_)

.. _328: pallets-eco/flask-sqlalchemy#328
.. _364: pallets-eco/flask-sqlalchemy#364
.. _373: pallets-eco/flask-sqlalchemy#373
.. _409: pallets-eco/flask-sqlalchemy#409
.. _443: pallets-eco/flask-sqlalchemy#443
.. _460: pallets-eco/flask-sqlalchemy#460
.. _461: pallets-eco/flask-sqlalchemy#461
.. _467: pallets-eco/flask-sqlalchemy#467

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[ivan-c]

@pbugni Think this fixes it, mind taking a look?