Merge pull request #17 from tokudu/fix-stats-tube

stats-tube can return NOT_FOUND according to the protocol spec

lib/beanstalk_client.js

@@ -466,7 +466,7 @@ BeanstalkClient.prototype.statsJob = BeanstalkClient.prototype.stats_job;
 BeanstalkClient.prototype.stats_tube = function(tube) {
 	return this.command({
 		command: 'stats-tube '+tube+'\r\n',
-		expected: 'OK',
+		expected: ['OK', 'NOT_FOUND'],
 		is_yaml: 1
 	});
 };