try using dj-database-url package

requirements.txt

@@ -2,4 +2,5 @@ astroid==2.2.5
 Django==2.1.7
 selenium==3.141.0
 gunicorn==19.9.0
-psycopg2==2.8.3
\ No newline at end of file
+psycopg2==2.8.3
+dj-database-url==0.5.0
\ No newline at end of file

superlists/settings.py

+import dj_database_url
 """
 Django settings for superlists project.
 
@@ -80,15 +81,13 @@ WSGI_APPLICATION = 'superlists.wsgi.application'
 
 DATABASES = {
     'default': {
-        'ENGINE': 'django.db.backends.postgresql_psycopg2',
-        'NAME': 'todo_list',  # os.environ.get('DB_NAME', ''),
-        'USER': 'rahmania',  # os.environ.get('DB_USER', ''),
-        'PASSWORD': 'asdasd123',  # os.environ.get('DB_PASS', ''),
-        'HOST': 'localhost',
-        'PORT': '5432'
+        'ENGINE': 'django.db.backends.sqlite3',
+        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
     }
 }
 
+db_from_env = dj_database_url.config(conn_max_age=500)
+DATABASES['default'].update(db_from_env)
 
 # Password validation
 # https://docs.djangoproject.com/en/2.1/ref/settings/#auth-password-validators