Update Swift to 4.0

Updates the GitCommit for Swift 4.0 as tags 4.0, latest. Also removes the latest tag from swift 3

library/swift

@@ -2,7 +2,10 @@ Maintainers: Haris Amin <[email protected]> (@hamin),
              Thomas Catterall <[email protected]> (@swizzlr)
 GitRepo: https://github.com/swiftdocker/docker-swift.git
 
-Tags: 3.1.0, 3.1, 3, latest
+Tags: 4.0, latest
+GitCommit: 545b8629ffe1f9785298203cf1382711cc2ac302
+
+Tags: 3.1.0, 3.1, 3
 GitCommit: ef9aa534705fc8ab4258c539f6304072ebae9613
 
 Tags: 3.0.2, 3.0