fixed test which did not bounce properly when convergence setting was low

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/branches/MATH_2_0@676620 13f79535-47bb-0310-9956-ffa450edef68

src/test/org/apache/commons/math/ode/nonstiff/TestProblem4.java

@@ -113,6 +113,7 @@ public class TestProblem4
     }
   
     public void resetState(double t, double[] y) {
+      y[0] = -y[0];
       y[1] = -y[1];
     }