Update README.md (#229)

fix libGDX unavailable url

Author: likfe

README.md

@@ -1,5 +1,5 @@
 # About
-Packages your JAR, assets and a JVM for distribution on Windows, Linux and macOS, adding a native executable file to make it appear like a native app. Packr is most suitable for GUI applications, such as games made with [libGDX](http://libgdx.badlogicgames.com/).
+Packages your JAR, assets and a JVM for distribution on Windows, Linux and macOS, adding a native executable file to make it appear like a native app. Packr is most suitable for GUI applications, such as games made with [libGDX](https://libgdx.com/).
 
 On the topic of games, Packr version 2.4.2+ supports Java 14 and the [Z garbage collector](https://wiki.openjdk.java.net/display/zgc/Main) has been verified to work. Because who doesn't want GC pause times guaranteed to not exceed 10ms with work in progress for sub 1ms GC pauses. When bundling Java 14+ make sure to use `--useZgcIfSupportedOs` instead of passing `--vmargs XX:+UseZGC` because versions of Windows before Windows 10 1803 are not supported by the Z garbage collector.