mysql JSONSet Build bool type to 1/0，expected true/false

## GORM Playground Link

https://github.com/go-gorm/datatypes/pull/284

问题描述
```golang
set := datatypes.JSONSet("object")
set.Set("test_bool", meta.TestBool)
db.....Update("object", set)

```

执行后结果

```
{ "test_bool": 1}

```

修改
bool 类型直接构造为 SQL，而不是通过 statement AddVar 替换为占位符