update screenshot link in README

Author: robhagemans

README.md

@@ -12,7 +12,7 @@ PC-BASIC is free and open source software released under the GPL version 3.
 
 See also the [PC-BASIC home page](http://robhagemans.github.io/pcbasic/).
 
-![](https://robhagemans.github.io/pcbasic/screenshots/pcbasic.png)
+![](https://robhagemans.github.io/pcbasic/screenshots/pcbasic-2.0.png)
 
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