Make gradle integration proguard test JDK 11 compatible

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/interopWithProguarded/lib/build.gradle

@@ -24,7 +24,13 @@ configurations {
 task obfuscate(type: proguard.gradle.ProGuardTask, dependsOn: jar) {
     injars "${jar.archivePath}"
     outjars "$buildDir/proguard/out.jar"
-    libraryjars "$System.env.JAVA_HOME/jre/lib/rt.jar"
+
+    if (JavaVersion.current().isJava9Compatible()) {
+        libraryjars "${System.getProperty('java.home')}/jmods"
+    } else {
+        libraryjars "${System.getProperty('java.home')}/lib/rt.jar"
+    }
+
     libraryjars configurations.named("resolvableImplementation")
 
     dontobfuscate