Fix linter issues

Author: Golf Player

nbclient/client.py

@@ -231,7 +231,7 @@ class NotebookClient(LoggingConfigurable):
         default_value=None,
         allow_none=True,
         help=dedent("""
-        Called after the kernel manager and kernel client are setup, and cells 
+        Called after the kernel manager and kernel client are setup, and cells
         are about to execute.
         Called with kwargs `kernel_id`.
         """),
@@ -260,7 +260,7 @@ class NotebookClient(LoggingConfigurable):
         default_value=None,
         allow_none=True,
         help=dedent("""
-        A callable which executes when a cell execution results in an error. 
+        A callable which executes when a cell execution results in an error.
         This is executed even if errors are suppressed with `cell_allows_errors`.
         Called with kwargs `cell`, and `cell_index`.
         """),