title: negative lookahead regex on elasticsearch
body: <p>I'm trying to do a negative lookahead on an elasticsearch query, 
  the regex is: </p>
  
  <pre><code>(?!.*charge)(?!.*encode)(?!.*relate).*night.*
  </code></pre>
  
  <p>the text that I'm matching against is: </p>
  
  <blockquote>
    <p>credited back on night stay, still having issues with construction. 
    causing health issues due to a chemical being sprayed and causes eyes
    to irritated.</p>
  </blockquote>
  
  <p>I didn't get any lucky. Can someone give a hand? </p>
  
  <p>ES query: </p>
  
  <pre><code>  "query": {
      "filtered": {
        "query": {
          "bool": {
            "must_not": [
              {
                "regexp": {
                  "message": {
                    "value": "(?!.*charge)(?!.*encode)(?!.*relate).*night.*",
                    "flags_value": 65535
                  }
                }
              }
            ]
          }
        },
        "filter": {
          "match": {
            "resNb": {
              "query": "462031152161",
              "type": "boolean"
            }
          }
        }
      }
    }
  </code></pre>