fix: cancel_futures arg not supported until 3.8

Author: jlwalke2

src/sasctl/core.py

@@ -1534,7 +1534,7 @@ def __enter__(self):
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         if self._pool is not None:
-            self._pool.shutdown(wait=False, cancel_futures=True)
+            self._pool.shutdown(wait=False)
 
     def __next__(self):
         if self._pool is None: