Restrict SQLAlchemy to 1.3

https://docs.sqlalchemy.org/en/14/changelog/migration_14.html

The previous SQLAlchemy version constraint in pyproject.toml,
`sqlalchemy = "^1.3.16"`, allowed SQLAlchemy 1.4 to be installed.
SQLAlchemy 1.4 includes many API changes, and should not be installed
until the back-end Python application logic has been updated.

This commit will update the version constraint to `sqlalchemy = "~1.3"`,
which allows further updates to SQLAlchemy 1.3, but not SQLAlchemy 1.4.
See https://semver.npmjs.com/ for a helpful demonstration of this.

This commit will also install `psycopg2` through SQLAlchemy for maximum
compatibility.

Author: br3ndonland

{{cookiecutter.project_slug}}/backend/app/pyproject.toml

@@ -16,9 +16,8 @@ tenacity = "^6.1.0"
 emails = "^0.5.15"
 raven = "^6.10.0"
 jinja2 = "^2.11.2"
-psycopg2-binary = "^2.8.5"
 alembic = "^1.4.2"
-sqlalchemy = "^1.3.16"
+sqlalchemy = {extras = ["postgresql_psycopg2binary"], version = "~1.3"}
 pytest = "^5.4.1"
 python-jose = {extras = ["cryptography"], version = "^3.1.0"}