update podspec + readme to prepare for 5.0.0 release w/ Swift 5 support

PinEntryView.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = 'PinEntryView'
-  s.version          = '4.0.0'
+  s.version          = '5.0.0'
   s.screenshot       = 'https://user-images.githubusercontent.com/2835199/36484248-9eb1673e-16e6-11e8-82af-75dc08539b5a.png'
   s.summary          = 'PinEntryView is a customizable view written in Swift that can be used to confirm alphanumeric pins.'
   s.description      = <<-DESC

README.md

@@ -1,6 +1,6 @@
 ![PinEntryView Logo](https://cloud.githubusercontent.com/assets/2835199/25503255/aa050598-2b67-11e7-89f7-b0fbc6da31ba.png)
 
-![Swift4.0](https://img.shields.io/badge/Swift-4.0-orange.svg?style=flat")
+![Swift5.0](https://img.shields.io/badge/Swift-5.0-orange.svg?style=flat")
 [![Platform](https://img.shields.io/cocoapods/p/PinEntryView.svg?style=flat)](http://cocoapods.org/pods/PinEntryView)
 [![Version](https://img.shields.io/cocoapods/v/PinEntryView.svg?style=flat)](http://cocoapods.org/pods/PinEntryView)
 [![License](https://img.shields.io/cocoapods/l/PinEntryView.svg?style=flat)](http://cocoapods.org/pods/PinEntryView)
@@ -48,7 +48,10 @@ To integrate `PinEntryView` into your Xcode project using CocoaPods, specify it
 pod 'PinEntryView'
 ```
 
-(For Swift 3.1, use `pod 'PinEntryView', '~> 1.0.0'` instead)
+_Legacy Support:_
+
+- For Swift 3.1, use `pod 'PinEntryView', '~> 1.0.0'` instead
+- For Swift 4, use `pod 'PinEntryView', '~> 4.0.0'` instead
 
 Then, run the following command: