modification

hi, I'm web engineer in japan.

I used your swift class.
He was very helpful.

I found error point. line160&166 

My dev env is Version 6.0.1 (6A317), maybe newest release version.

Please merge this change.

best regard.

```
Agent.swift:160:17: Optional type 'NSError!' cannot be used as a boolean; test for '!= nil' instead
```
![](http://i.gyazo.com/42802ae7b089ef093758b02c57ee48a4.png)