Fixed flake8 error in test_iostream.py

tests/test_iostream.py

@@ -53,6 +53,7 @@ def test_captured(capsys):
     assert stdout == ''
     assert stderr == msg
 
+
 def test_captured_large_string(capsys):
     # Make this bigger than the buffer used on the C++ side: 1024 chars
     msg = "I've been redirected to Python, I hope!"