title: new Date().getTimezoneOffset() returns the wrong time zone
body: <p>I am in Israel, so my offset right now should be <code>120</code>. Yet, when I use <code>new Date().getTimezoneOffset()</code>, I get back <code>-120</code>, so not just a daylight savings issue.
  Should I simply change every minus to plus and vice versa? I don't know what might be the case for users in other timezones.</p>
  
  <p>That's my function:</p>
  
  <pre><code>  firebase
      .database()
      .ref("words/" + newPostKey)
      .set({
        word,
        length: word.length,
        time_to_action: timeToAction,
        output: output,
        lang: project.lang,
        country: project.country,
        user: userUID,
        timestamp : Date.now(),
        timezone_offset : new Date().getTimezoneOffset()
      });
  </code></pre>
  
  <p>and <code>timezone_offset</code> is what gets saved as <code>-120</code>. I am in Tel Aviv.</p>