Adjust DownstreamCreatorIT to work with latest Gerrit core

Change-Id: Iac5e04a5c8e05fb29d2ae467a4708b08d8a007bd
diff --git a/src/test/java/com/googlesource/gerrit/plugins/automerger/DownstreamCreatorIT.java b/src/test/java/com/googlesource/gerrit/plugins/automerger/DownstreamCreatorIT.java
index d04fd1d..5848852 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/automerger/DownstreamCreatorIT.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/automerger/DownstreamCreatorIT.java
@@ -251,7 +251,7 @@
 
     // Freeze time so that the merge commit from left->bottom and right->bottom have same SHA
     TestTimeUtil.resetWithClockStep(0, TimeUnit.MILLISECONDS);
-    TestTimeUtil.setClock(new Timestamp(TestTimeUtil.START.getMillis()));
+    TestTimeUtil.setClock(new Timestamp(TestTimeUtil.START.toEpochMilli()));
     // After we upload our config, we upload a new patchset to create the downstreams.
     PushOneCommit.Result result = createChange("subject", "filename2", "echo Hello", "sometopic");
     TestTimeUtil.useSystemTime();