fix rss dependency and handling of nil author (#35) Co-authored-by: Andrea Selva <selva.andre@gmail.com>

set default_codec doc attribute 

[skip ci] update gemspec summary 

Version bump For elastic/logstash#7993 [ci skip]

bump patch level for doc generation 

dependency logstash-core-plugin-api >= 1.60 <= 2.99 

make travis use openjdk8 Fixes #18

dependency logstash-core-plugin-api ~> 1.0 

Bumping up version + adding to changelog Fixes #15

dependency logstash-core >= 2.0.0.beta2 < 3.0.0