Update README.md

Updated swift version 4 -> 5

Author: TonioMacaronio

README.md

@@ -3,7 +3,7 @@
 # web3swift
 
 [![Build Status](https://travis-ci.com/matter-labs/web3swift.svg?branch=develop)](https://travis-ci.com/matter-labs/web3swift)
-[![Swift](https://img.shields.io/badge/Swift-4.0-orange.svg?style=flat)](https://developer.apple.com/swift/)
+[![Swift](https://img.shields.io/badge/Swift-5.0-orange.svg?style=flat)](https://developer.apple.com/swift/)
 [![Platform](https://img.shields.io/cocoapods/p/web3swift.svg?style=flat)](http://cocoapods.org/pods/web3swift)
 [![CocoaPods Compatible](https://img.shields.io/cocoapods/v/web3swift.svg?style=flat)](http://cocoapods.org/pods/web3swift)
 [![Carthage Compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)