fixed wrong variable name in sleep filter
fixed wrong variable name in sleep filter

wrong variable name leads to exceptions when using the sleep filter with
replay option

Aloomaio/logstash-kafka,opentable/logstash-kafka,joekiller/logstash-kafka,opentable/logstash-kafka,Aloomaio/logstash-kafka,joekiller/logstash-kafka,tinglinux/logstash-kafka,tinglinux/logstash-kafka