Merge pull request #591 from morrme/rectangles-remove-final

rectangles: remove "final" from class declaration

exercises/rectangles/src/test/java/RectangleCounterTest.java

 
 import static org.junit.Assert.assertEquals;
 
-public final class RectangleCounterTest {
+public class RectangleCounterTest {
 
     private RectangleCounter rectangleCounter;