#14692 Fix json docs to reflect changes in json.load
#14692 Fix json docs to reflect changes in json.load

The behaviour of the parse_constant callback changed insofar that 'null',
'true', 'false' don't trigger its call anymore.

Patch by Serhiy Storchaka

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator