bpo-30621: Update Input Output Tutorial Example(GH-2074)

 import json before using json module 
diff --git a/Doc/tutorial/inputoutput.rst b/Doc/tutorial/inputoutput.rst
index bad0302..92f439c 100644
--- a/Doc/tutorial/inputoutput.rst
+++ b/Doc/tutorial/inputoutput.rst
@@ -412,6 +412,7 @@
 If you have an object ``x``, you can view its JSON string representation with a
 simple line of code::
 
+   >>> import json
    >>> json.dumps([1, 'simple', 'list'])
    '[1, "simple", "list"]'