Fix shortcut target path when using script

In script mode, previously the shortcut would use the entire path
provided in the config file rather than the filename of the script,
resulting in a broken path and useless shortcut.

nsist/__init__.py

@@ -316,8 +316,9 @@ if __name__ == '__main__':
 
                 target = '$INSTDIR\\Python\\python{}.exe'
                 sc['target'] = target.format('' if sc['console'] else 'w')
+                sc['script'] = os.path.basename(sc['script'])
                 sc['parameters'] = '"%s"' % ntpath.join('$INSTDIR', sc['script'])
-                files.add(os.path.basename(sc['script']))
+                files.add(sc['script'])
 
             shutil.copy2(sc['icon'], self.build_dir)
             sc['icon'] = os.path.basename(sc['icon'])