Swift documentation doesn't mention the need to cast return value of `injector.instance`

[lalunamel]

For example, in the Swift section there is a line

let controller = injector.getInstance(MyViewController.self)

which compiles, but doesn't allow you to use the variable controller because it is an unknown type.

In order for that variable to be recognized as an instance of MyViewController it should be

let controller = injector.getInstance(MyViewController.self) as! MyViewController OR let controller: MyViewController = injector.getInstance(MyViewController.self) as! MyViewController

As someone new to Swift, that bit tripped me up.

[akitchen]

Thanks for the fix in #60