Test the Gradle plugin against Gradle 4.1 and 4.2

Closes gh-10417

Author: wilkinsona

spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/junit/GradleCompatibilitySuite.java

@@ -38,8 +38,8 @@
  */
 public final class GradleCompatibilitySuite extends Suite {
 
-	private static final List<String> GRADLE_VERSIONS = Arrays.asList("default",
-			"4.1-rc-1");
+	private static final List<String> GRADLE_VERSIONS = Arrays.asList("default", "4.1",
+			"4.2");
 
 	public GradleCompatibilitySuite(Class<?> clazz) throws InitializationError {
 		super(clazz, createRunners(clazz));