mappingArray失败,求解惑

尝试JsonString mapping modelArray 的时候失败，求解惑。。

### testModel code（export from jsonData）
```swift
struct TestModel : HandyJSON{

var result : Result?
var success : String?


}

struct Result : HandyJSON{

var disline : String?
var lists : List?
var page : String?
var totline : String?

}

struct List : HandyJSON{

var sh600000 : Sh600000?

}

struct Sh600000 : HandyJSON{

var buy1M : String?
var buy1N : String?
}
```
### defind func code (extension moya.response)
```swift
public func mapArray(_ type: T.Type ,path:String) throws -> [T] {

guard let ary = [T].deserialize(from: try mapString(), designatedPath:path) else {
throw MoyaError.jsonMapping(self)
}
return ary.flatMap{ $0.flatMap { $0 }}
}
```
### call func code (by moya)
```swift
TestApiProvider.request(.test) { Result in

switch Result {
case let .success(response):
var model:[List] = [List]()
do {

model = try response.mapArray(List.self, path: "result.lists")
print(model as Any)
} catch {

}
break
case .failure(_):
break
}
}
```
结果是调用时总是[T].deserialize转换失败（mapJsonStr是成功），抛出异常。
对Swift和HandyJSON还不是很了解，是我的用法错了吗？

Start at the response.mapArray(List.self, path: "result.lists") call and compare the supplied TestModel, Result, List, and Sh600000 structures with the JSON passed to mapString(). Reproduce the failure and inspect the designated path and deserialization result; done means the cause is identified and the example either maps successfully or is clearly documented as unsupported.

Written by the indexing model from the issue text.