Rename SPRING_CLASS_RULE fields to springClassRule

src/docs/asciidoc/testing.adoc

@@ -3627,7 +3627,7 @@ demonstrates the proper way to declare these rules in an integration test.
 public class IntegrationTest {
 
    @ClassRule
-   public static final SpringClassRule SPRING_CLASS_RULE = new SpringClassRule();
+   public static final SpringClassRule springClassRule = new SpringClassRule();
 
    @Rule
    public final SpringMethodRule springMethodRule = new SpringMethodRule();