change __heartbeat__ timeout to 5s - the same as what zeus allows in production

lib/heartbeat.js

@@ -10,7 +10,7 @@ url = require('url');
 // the path that heartbeats live at
 exports.path = '/__heartbeat__';
 
-const checkTimeout = 10000;
+const checkTimeout = 5000;
 
 // a helper function to set up a heartbeat check
 exports.setup = function(app, options, cb) {