title: Sapper back button not working after history pushstate function
body: <p>I'm using following versions of Sapper and Svelte:</p>
  
  <pre><code>"sapper": "^0.27.0",
  "svelte": "^3.0.0"
  </code></pre>
  
  <p>After updating the url using <code>history.pushState()</code> function, and then navigating to other page. The back button is not taking back to the url changed by <code>history.pushState()</code></p>