title: How to use moment-tz.js to parse tz like "GMT-08:00"
body: <p>I try to run this js</p>
  
  <pre><code>return function(milliSeconds, timeZoneId) {
      if (milliSeconds == 0) {
          return "";
      }
      var now = moment();
  
      return now.tz(timeZoneIdm, milliSeconds).format('MMM d, yyyy H:mm:ss'); 
  }
  </code></pre>
  
  <p>For example with this input:</p>
  
  <pre><code>milliSeconds = "1524578400000"
  
  timezoneId = "GMT-08:00"
  </code></pre>
  
  <p>it fails for parsing <code>"GMT-08:00"</code>. Anyway can I adjust it to work?</p>