doc: Use super() in subclassed JSONEncoder examples (pythonGH-115565)

Replace calls to `json.JSONEncoder.default(self, obj)`
by `super().default(obj)` within the examples of the documentation.

Author: phorward

Doc/library/json.rst

@@ -106,7 +106,7 @@ Extending :class:`JSONEncoder`::
     ...         if isinstance(obj, complex):
     ...             return [obj.real, obj.imag]
     ...         # Let the base class default method raise the TypeError
-    ...         return json.JSONEncoder.default(self, obj)
+    ...         return super().default(obj)
     ...
     >>> json.dumps(2 + 1j, cls=ComplexEncoder)
     '[2.0, 1.0]'
@@ -504,7 +504,7 @@ Encoders and Decoders
             else:
                 return list(iterable)
             # Let the base class default method raise the TypeError
-            return json.JSONEncoder.default(self, o)
+            return super().default(o)
 
 
    .. method:: encode(o)

Lib/json/encoder.py

@@ -174,7 +174,7 @@ def default(self, o):
                 else:
                     return list(iterable)
                 # Let the base class default method raise the TypeError
-                return JSONEncoder.default(self, o)
+                return super().default(o)
 
         """
         raise TypeError(f'Object of type {o.__class__.__name__} '