requirements/base: simplify sqlalchemy version condition

requirements/base.txt

@@ -3,6 +3,6 @@ prompt-toolkit>=3.0.2
 pyaml>=19.4.1
 PyYAML>=5.1.2
 Pygments>=2.6.0
-SQLAlchemy>=1.3.11,<2.0.0
+SQLAlchemy<2.0.0
 tabulate>=0.8.5
 wheel>=0.35.0