title: elastic search regex query to search string starts with number
body: <p>i am not able to search string start with number</p>
  
  <pre><code>PUT music/song/1?refresh
  {
      "suggest" : [
          {
              "input": "123hello",
              "weight" : 3
          }
      ]
  }
  </code></pre>
  
  <p>i have tried the following regex query </p>
  
  <pre><code>POST music/_search?pretty
  {
      "suggest": {
          "song-suggest" : {
              "regex" : "^[0-9].*$",
              "completion" : {
                  "field" : "suggest"
              }
          }
      }
  }
  </code></pre>