[README] Update version numbers in README to 4.0

[ci skip]

Author: ide

README.md

@@ -12,11 +12,11 @@ Linking the Framework
 
 Synchronized is available through [CocoaPods](http://cocoapods.org). To install it, simply add the following line to your Podfile:
 
-    pod "Synchronized", "~> 2.0"
-    
+    pod "Synchronized", "~> 4.0"
+
 You can also use [Carthage](https://github.com/Carthage/Carthage) to fetch it from GitHub:
 
-    github "ide/Synchronized" ~> 2.0
+    github "ide/Synchronized" ~> 4.0
 
 Once the framework is linked this Swift code should compile:
 ```swift