More Cocoapod compatible

Hi, 

This is a very nice Alert I'm using in my project, I would like to recommend to structure the project as CocoaPods compatible that should pass all the validations of the command:

```
pod lib lint SweetAlert.podspec
```

I've created a branch develop in my fork, if you are interested in a PR (https://github.com/codestergit/SweetAlert-iOS/pull/44).

Thanks,
J.
