pjson not returning expected value with Swift

Using the latest version of chisel from Homebrew. When I use pjson on a `[String: String]` dictionary in Swift, it doesn't appear to work.

```
(lldb) pjson response
error: error: use of undeclared identifier 'response'
error: error: use of undeclared identifier 'None'
None
```

Happy to help contribute a fix if this only works for Objective-C!