ci: Update to Swift 5.1

Support Swift 5 (Kitura#73)

Update to Swift 4.1 and BlueSocket 1.0 (Kitura#64)

Update to swift 403 (Kitura#62)

* Update to swift 403

* Update to swift 403

* README update

Updated to Swift 4.0 (Kitura#61)

* Updated to Swift 4

* Deleted Package.pins

* Finalised conversion to Swift 4 only

* Migration to Swift 4.0.2

Merge pull request Kitura#60 from IBM-Swift/swift4

Swift4