Readme: Update requirements for astor library version

Author: khalim19

README.md

@@ -25,8 +25,7 @@ Requirements
 
 * This script is written as a GIMP plug-in and therefore requires GIMP, version
 2.8 or later.
-* [astor](https://github.com/berkerpeksag/astor) library - not version 0.5, but
-  preferably the latest revision from the repository.
+* [astor](https://github.com/berkerpeksag/astor) library - version 0.6 or later.
 
 
 Installation