Add Type to relationshipWasNil RuneError

[seanmiller802]

No description provided.

[joshuawright11]

Awesome! Can we pass the type to the error function? Will prevent callers of the function from passing in a String that isn't actually a type.

public static func relationshipWasNil<M: Model>(type: M.Type) -> RuneError {
    RuneError("This non-optional relationship to \(type) has no matching models.")
}

Then call like...

RuneError.relationshipWasNil(type: Self.self)