Update for Swift 4.2.
Update for Swift 4.2.

* Remove the top code snippet, as per instructions.
* Remove use of deprecated `characters` property.

jawwad/swift-algorithm-club,hollance/swift-algorithm-club,jawwad/swift-algorithm-club,raywenderlich/swift-algorithm-club,raywenderlich/swift-algorithm-club,raywenderlich/swift-algorithm-club,jawwad/swift-algorithm-club