title: String.hashValue not unique after reset app when build in Xcode 10
body: <p>I have a "get hash of string by <code>String.hashValue</code>" code, that I added it below. This code worked well in Xcode 9.4.1.</p>
  
  <p>Worked well means that whenever I close app and re-open it, the result of <code>hashValue</code> is same (unique)</p>
  
  <pre><code>private func cacheName(of url: String) -&gt; String {
      // The url is url of a png image, for example www.imageurl.com/image.png
      return "\(url.hashValue)"
  }
  </code></pre>
  
  <p>When I build my Project in Xcode 10 the result changes everytime I restart the app (close and open app again). The version of iOS, device, Swift version is same. So I think the problem is Xcode 10 has change something that effect to the <code>hashValue</code> (maybe configure when build app ??)</p>
  
  <p>If I use the <code>String.hash</code> instead of, it works well. But in the previous version, I saved the <code>hashValue</code> result, so I don't want to change it.</p>
  
  <p>How can I keep the result of <code>String.hashValue</code> unique in every time. Or any suggestion would be appreciated</p>