BUG: replace int64 dtype with bool coerces to int64
```
# NG
s = pd.Series([1, 2, 3])
s.replace(2, True)
#0    1
#1    1
#2    3
# dtype: int64
```

If target has `object` dtype, it works.

```
s = pd.Series(['x', 2, 3])
s.replace(2, True)
#0       x
#1    True
#2       3
# dtype: object
```
