fix error introduced to dbwriter heartbeat - inverted health value - issue #566

bin/dbwriter

@@ -65,7 +65,9 @@ logger.info("dbwriter starting up");
 // This is in front of logging on purpose.  see issue #537
 heartbeat.setup(app, function(cb) {
   // ping the database to verify we're really healthy.
-  db.ping(cb);
+  db.ping(function(e) {
+    cb(e === undefined);
+  });
 });
 
 // logging!  all requests other than __heartbeat__ are logged