Update JCTF class path after gradle upgrade.

Change-Id: I7d5cffebef86fbd21b584976870dd08069550605
diff --git a/src/test/java/com/android/tools/r8/R8RunArtTestsTest.java b/src/test/java/com/android/tools/r8/R8RunArtTestsTest.java
index 6d34f44..5b5cf9d 100644
--- a/src/test/java/com/android/tools/r8/R8RunArtTestsTest.java
+++ b/src/test/java/com/android/tools/r8/R8RunArtTestsTest.java
@@ -104,7 +104,7 @@
   private static final String JCTF_COMMON_JAR = "build/libs/jctfCommon.jar";
 
   // Parent dir for on-the-fly compiled jctf dex output.
-  private static final String JCTF_TESTS_PREFIX = "build/classes/jctfTests";
+  private static final String JCTF_TESTS_PREFIX = "build/classes/java/jctfTests";
   private static final String JCTF_TESTS_LIB_PREFIX =
       JCTF_TESTS_PREFIX + "/com/google/jctf/test/lib";
   private static final String JUNIT_TEST_RUNNER = "org.junit.runner.JUnitCore";