fix flake8

Author: rohitsanj

nbclient/exceptions.py

@@ -70,7 +70,7 @@ def from_cell_and_msg(cls, cell, msg):
             ),
             ename=msg.get('ename', '<Error>'),
             evalue=msg.get('evalue', '')
-    )
+        )
 
 
 exec_err_msg = u"""\