Use logger built-in format

Change-Id: Ibc0f5260dbbd1f5c7ff51fdaf487e674dc1a0288
diff --git a/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatConfig.java b/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatConfig.java
index 07f9c43..4031a4e 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatConfig.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatConfig.java
@@ -52,7 +52,7 @@
   private void load(File configPath) throws ConfigInvalidException, IOException {
     FileBasedConfig cfg = new FileBasedConfig(configPath, FS.DETECTED);
     if (!cfg.getFile().exists() || cfg.getFile().length() == 0) {
-      logger.debug("No " + cfg.getFile() + " or empty; using all default values");
+      logger.debug("No {} or empty; using all default values", cfg.getFile());
       return;
     }
 
diff --git a/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatDaemon.java b/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatDaemon.java
index 8a5b6b8..111f447 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatDaemon.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatDaemon.java
@@ -51,7 +51,7 @@
   @Override
   public void start() {
     timer.schedule(new HeartbeatTask(), 0, config.getDelay());
-    logger.info("Initialized to send heartbeat event every " + config.getDelay() + " milliseconds");
+    logger.info("Initialized to send heartbeat event every {} milliseconds", config.getDelay());
   }
 
   @Override