fix broken test

Author: kaisecheng

lib/logstash/inputs/redis.rb

@@ -3,6 +3,7 @@
 require "logstash/inputs/base"
 require "logstash/inputs/threadable"
 require 'redis'
+require "stud/interval"
 
 # This input will read events from a Redis instance; it supports both Redis channels and lists.
 # The list command (BLPOP) used by Logstash is supported in Redis v1.3.1+, and