Fix error message in RemoteReader.

Change-Id: I2b2780fe11e9757c24cf1f3c68bae0a76797357d

src/main/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java b/src/main/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java
index 9672b6d..1d1a33e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/supermanifest/SuperManifestRefUpdatedListener.java
@@ -418,7 +418,7 @@
         Repository repo = openRepository(repoName);
         Ref ref = repo.findRef(refName);
         if (ref == null || ref.getObjectId() == null) {
-          log.warn("%s: repo %s cannot resolve %s", repo, refName);
+          log.warn(String.format("in repo %s: cannot resolve ref %s", uriStr, refName));
           return null;
         }