Fix Swift PM Semantic Version (#3081)

* Fix semantic version string in README

* Swap dependency specifier to enum-driven approach

README.md

@@ -103,7 +103,7 @@ Once you have your Swift package set up, adding Alamofire as a dependency is as
 
 ```swift
 dependencies: [
-    .package(url: "https://github.com/Alamofire/Alamofire.git", from: "5.0")
+    .package(url: "https://github.com/Alamofire/Alamofire.git", .upToNextMajor(from: "5.0.0"))
 ]
 ```