Update README.md

Author: paulofaria

README.md

@@ -138,7 +138,7 @@ The following strategies are available:
 
 This project is released under the MIT license. See [LICENSE](LICENSE) for details.
 
-[swift-badge]: https://img.shields.io/badge/Swift-3.0-orange.svg?style=flat
+[swift-badge]: https://img.shields.io/badge/Swift-4.0-orange.svg?style=flat
 [swift-url]: https://swift.org
 [mit-badge]: https://img.shields.io/badge/License-MIT-blue.svg?style=flat
 [mit-url]: https://tldrlegal.com/license/mit-license