ReplicationTaskStorage: fix format by adding conversion

See https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html

Change-Id: I68e4107e2b06951cce39befd4af9ee2918108424
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
index 6884185..0e0f787 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
@@ -74,7 +74,7 @@
         logger.atFine().log("File %s not found while reading task", file);
       } catch (IOException e) {
         if (!e.getMessage().equals("Is a directory")) {
-          logger.atSevere().withCause(e).log("Error while reading task %", file);
+          logger.atSevere().withCause(e).log("Error while reading task %s", file);
         }
       }
       return Optional.empty();