ArrayType in extension where clause

extension Array where Element: _ArrayType, Element.Generator.Element: Any {    func transpose() -> [Element] {        if self.isEmpty { return [Element]() }        let count = self[0].count        var out = [Element](repeating: Element(), count: count)        for outer in self {            for (index, inner) in outer.enumerated() {                out[index].append(inner)            }        }        return out    }}

I am getting this error in Swift 3.0 after converting it from Swift 2.2. The elements of the array are also array. So how to define it in Swift 3.0?