Fix syntax error in NamedTuple example
$ python3 -c "typing.NamedTuple('NT', [('a': int, 'b': Tuple[str, ...])])"
File "<string>", line 1
typing.NamedTuple('NT', [('a': int, 'b': Tuple[str, ...])])
^
SyntaxError: invalid syntax
@@ -413,7 +413,7 @@ Availability:
```python
# input
-NT = typing.NamedTuple('NT', [('a': int, 'b': Tuple[str, ...])])
+NT = typing.NamedTuple('NT', [('a', int), ('b', Tuple[str, ...])])
D1 = typing.TypedDict('D1', a=int, b=str)
