Mark `bool` as MessagePack serializable
As `bool` values can be serialized by MessagePack (see code below), mark
them as such in `_is_msgpack_serializable`.
```python
In [1]: import msgpack
In [2]: (msgpack.dumps(False), msgpack.dumps(True))
Out[2]: (b'\xc2', b'\xc3')
In [3]: (msgpack.loads(b'\xc2'), msgpack.loads(b'\xc3'))
Out[3]: (False, True)
```
@@ -548,6 +548,7 @@ def _is_msgpack_serializable(v):
typ = type(v)
return (
typ is str
+ or typ is bool
or typ is int
or typ is float
or isinstance(v, dict)
