Bump version to 3.1.0 and add release notes

Author: magnusbaeck

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 3.1.0
+ - feature: Add 'metadata' option that enables inclusion of the @metadata field in the output.
+
 ## 3.0.6
   - Support flush method, see https://github.com/logstash-plugins/logstash-codec-json_lines/pull/35
 

logstash-codec-json_lines.gemspec

@@ -1,7 +1,7 @@
 Gem::Specification.new do |s|
 
   s.name            = 'logstash-codec-json_lines'
-  s.version         = '3.0.6'
+  s.version         = '3.1.0'
   s.licenses        = ['Apache License (2.0)']
   s.summary         = "Reads and writes newline-delimited JSON"
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program"