revert to use .raw instead of .keyword

In PR logstash-plugins#462 (comment)
we used `.keyword` to match ES's change in default behavior.

Both approaches, using `.keyword` to match ES for consistency and using `.raw` to match
existing logstash data has pros/cons. I think at this time it is wise to err on the side of
easy-upgrade-path so reverting this back to using `.raw` as before

Fixes logstash-plugins#466

Author: suyograo

lib/logstash/outputs/elasticsearch/elasticsearch-template-es5x.json

@@ -22,7 +22,7 @@
           "mapping" : {
             "type" : "text", "norms" : false,
             "fields" : {
-              "keyword" : { "type": "keyword" }
+              "raw" : { "type": "keyword" }
             }
           }
         }

spec/integration/outputs/templates_5x_spec.rb

@@ -1,6 +1,6 @@
 require_relative "../../../spec/es_spec_helper"
 
-describe "index template expected behavior", :integration => true, :version_less_than_5x => true do
+describe "index template expected behavior", :integration => true do
   subject! do
     require "logstash/outputs/elasticsearch"
     settings = {