Works fine with Swift 3, but with 4 (17 May 2017 snapshot) I get following error `'map' produces '[T]', not the expected contextual result type '[(Element)]'`

Swift_array_3vs4.swift

public extension Array where Element: FloatingPoint {
    func normalized(scale: Element) -> [Element] {
        guard let maxVal = self.max(), let minVal = self.min() else {
            return []
        }
        let diff = maxVal - minVal
        return self.map { val in
            ((val - minVal) / diff) * scale
        }
    }
}