title: Logstash float field does not been indexed
body: <p>The following is the configuration of logstash. When I input log into logstash, it works well as expected. All the field can be accepted by elasticsearch and the value and type of all fields is correct. However, when I view the log in kinana, it says that the cost field is not indexed so that it can't been visualized. While all the string fields are indexed. I want to visualize my float field. Anyone know what's the problem?</p>
  
  <pre><code>input {
      syslog {
          facility_labels=&gt;["local0"]
      port=&gt;515
      }
      stdin {}
  }
  
  filter{
      grok {
          overwrite =&gt; ["host", "message"]
          match =&gt; { "message" =&gt; " %{BASE10NUM:cost} %{GREEDYDATA:message}" }
  }
  mutate {
          convert =&gt; { "cost" =&gt; "float" }
      }
  }
  output {
      stdout{
          codec=&gt;rubydebug
      } 
      elasticsearch{  }
  }
  </code></pre>