Pin SQLAlchemy verison

Prior to this commit the requirements.txt did not pin a SQLAlchemy version.

Newer versions of SQLAlchemy removed the relation function used in the videos:
https://github.com/sqlalchemy/sqlalchemy/blob/d519bca7f953a0520cda79504dbc019e74e87b28/lib/sqlalchemy/orm/__init__.py#L143

The demo code uses relation instead of the newer relationship code, so in order
for the demo to work, users must install an older version of SQLAlchemy.

The videos used SQLAlchemy 1.2.10. This version is old enough that it is
incompatible with with Python 3.10. Trying to execute the demo code yields the
following error:

> AttributeError: module 'collections' has no attribute 'MutableMapping'

I found that version 1.2.19 was new enough to work with modern Python while
still maintaining the relation function. This commit pins 1.2.19 in the
requirements.txt file so other students do not run into the same issue.

Author: dhenschen

days/033-036-sqlalchemy-orm/demo/hovershare_app_final/requirements.txt

@@ -1 +1 @@
-sqlalchemy
+sqlalchemy==1.2.19

days/033-036-sqlalchemy-orm/demo/hovershare_app_starter/requirements.txt

@@ -1 +1 @@
-sqlalchemy
+sqlalchemy==1.2.19