Polish KotlinConventions

buildSrc/src/main/java/org/springframework/boot/build/KotlinConventions.java

@@ -43,17 +43,19 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile;
 class KotlinConventions {
 
 	void apply(Project project) {
-		project.getPlugins().withId("org.jetbrains.kotlin.jvm", (plugin) -> {
-			project.getTasks().withType(KotlinCompile.class, (compile) -> {
+		project.getPlugins().withId("org.jetbrains.kotlin.jvm",
+				(plugin) -> project.getTasks().withType(KotlinCompile.class, this::configure));
+	}
+
+	private void configure(KotlinCompile compile) {
 		KotlinJvmOptions kotlinOptions = compile.getKotlinOptions();
 		kotlinOptions.setApiVersion("1.6");
 		kotlinOptions.setLanguageVersion("1.6");
+		kotlinOptions.setJvmTarget("1.8");
 		kotlinOptions.setAllWarningsAsErrors(true);
 		List<String> freeCompilerArgs = new ArrayList<>(compile.getKotlinOptions().getFreeCompilerArgs());
 		freeCompilerArgs.add("-Xsuppress-version-warnings");
 		compile.getKotlinOptions().setFreeCompilerArgs(freeCompilerArgs);
-			});
-		});
 	}
 
 }