FIX: compatibility with SQLAlchemy < 1.4.0 (#105)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: DimitriPapadopoulos

jupyter_cache/cache/db.py

@@ -7,7 +7,13 @@
 from sqlalchemy import JSON, Column, DateTime, Integer, String, Text
 from sqlalchemy.engine import Engine, create_engine
 from sqlalchemy.exc import IntegrityError, OperationalError
-from sqlalchemy.orm import declarative_base, sessionmaker, validates
+
+try:
+    from sqlalchemy.orm import declarative_base  # sqlalchemy >= 1.4.0
+except ImportError:
+    from sqlalchemy.ext.declarative import declarative_base  # sqlalchemy < 1.4.0
+
+from sqlalchemy.orm import sessionmaker, validates
 from sqlalchemy.sql.expression import desc
 
 from jupyter_cache import __version__