Adapt to change in Gerrit core

Change Id93e378be changed the signature of
MergeValidationListener#onPreMerge.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I4aba0e0fdd33a8124edd847f0a0e334d6bf29a7a
diff --git a/src/main/java/com/googlesource/gerrit/plugins/automerger/MergeValidator.java b/src/main/java/com/googlesource/gerrit/plugins/automerger/MergeValidator.java
index efd3959..6a27eeb 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/automerger/MergeValidator.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/automerger/MergeValidator.java
@@ -27,6 +27,7 @@
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.git.CodeReviewCommit;
+import com.google.gerrit.server.git.CodeReviewCommit.CodeReviewRevWalk;
 import com.google.gerrit.server.git.validators.MergeValidationException;
 import com.google.gerrit.server.git.validators.MergeValidationListener;
 import com.google.gerrit.server.project.ProjectState;
@@ -62,6 +63,7 @@
   @Override
   public void onPreMerge(
       Repository repo,
+      CodeReviewRevWalk revWalk,
       CodeReviewCommit commit,
       ProjectState destProject,
       BranchNameKey destBranch,