Remove any mention of specific Swift version

This project is not so cutting edge anymore that it only works with the latest Swift versions.

Also ignore `.swift-version`, so it still can be used locally.

Author: kareman

.gitignore

@@ -124,3 +124,5 @@ iOSInjectionProject/
 default.profraw
 *.xcodeproj
 #Playground/MyPlayground.playground/
+
+.swift-version

.swift-version

@@ -1,12 +1,11 @@
 <p align="center">
-   <a href="https://developer.apple.com/swift/">
-      <img src="https://img.shields.io/badge/Swift-5.3-orange.svg?style=flat" alt="Swift 5.3">
-   </a>
    <a href="https://github.com/apple/swift-package-manager">
       <img src="https://img.shields.io/badge/Swift%20Package%20Manager-compatible-brightgreen.svg" alt="SPM">
    </a>
+   <img src="https://img.shields.io/badge/Linux-compatible-brightgreen" alt="Linux">
 </p> 
 
+
 # Patterns
 
 Patterns is a Swift library for Parser Expression Grammars (PEGs). It can be used to create expressions similar to regular expressions (like regex’es) and grammars (for parsers).