Fix in previous improvement to prism-auto.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@10594 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/etc/scripts/prism-auto

@@ -678,4 +678,4 @@ for arg in args:
     else:
         print "Error: File/directory " + arg + " does not exist"
 if options.nailgun:
-    subprocess.Popen(["ngprism", "stop"]).wait()
+    subprocess.Popen([options.ngprism, "stop"]).wait()