Updated suggested version in readme

Author: dimitribouniol

README.md

@@ -30,7 +30,7 @@ Please check the [releases](https://github.com/mochidev/swift-webpush/releases)
 dependencies: [
     .package(
         url: "https://github.com/mochidev/swift-webpush.git", 
-        .upToNextMinor(from: "0.3.3")
+        .upToNextMinor(from: "0.4.0")
     ),
 ],
 ...