use SAT solver that's available everywhere for this example

--- a/src/HOL/Nitpick_Examples/Refute_Nits.thy	Tue Nov 17 13:50:46 2009 +0100
+++ b/src/HOL/Nitpick_Examples/Refute_Nits.thy	Tue Nov 17 13:51:16 2009 +0100
@@ -17,7 +17,7 @@
 nitpick [expect = genuine] 2
 nitpick [expect = genuine]
 nitpick [card = 5, expect = genuine]
-nitpick [sat_solver = MiniSat, expect = genuine] 2
+nitpick [sat_solver = SAT4J, expect = genuine] 2
 oops
 
 subsection {* Examples and Test Cases *}