HeartbeatDaemon: Use Logger's built-in String formatting

Also fix typo in log message.

Change-Id: I1419bfa2ce27f33d8dfda40d65e3d83ee18882ee
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 111f447..63c2f84 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatDaemon.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/heartbeat/HeartbeatDaemon.java
@@ -66,7 +66,7 @@
       try {
         dispatcher.get().postEvent(new HeartbeatEvent());
       } catch (OrmException e) {
-        logger.error("Failed to post hearbeat event: " + e.getMessage(), e);
+        logger.error("Failed to post heartbeat event: {}", e.getMessage(), e);
       }
     }
   }