Required params "key" and "data_type" not documented as mandatory.

Config parameters `key` and `data_type` are [required](https://github.com/logstash-plugins/logstash-input-redis/blob/master/lib/logstash/inputs/redis.rb#L42), but [listed as optional in the docs](https://www.elastic.co/guide/en/logstash/master/plugins-inputs-redis.html#_synopsis_31).

A glitch in the document generator?
