Stop using JGit's deprecated Repository#peel method

Change-Id: I36347c8f55dea11ae0c582854927cce66cfb2953
diff --git a/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java b/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java
index dadc28f..d202b71 100644
--- a/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java
+++ b/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java
@@ -384,7 +384,7 @@
           return null;
         }
 
-        ref = repo.peel(ref);
+        ref = repo.getRefDatabase().peel(ref);
         ObjectId id = ref.getPeeledObjectId();
         return id != null ? id : ref.getObjectId();
       } catch (RepositoryNotFoundException e) {