message: update ledger tutorial
diff: <div uk-grid *ngIf="selectedImportOption === 'ledger'" class="uk-margin-top">
  <div class="uk-width-1-1">
  <p>
  - Make sure you have the Nano app installed, then connect your ledger device via USB (Chrome/Opera only). <a href="http://blog.nanovault.io/guides/use-your-ledger-device-with-nanovault/" target="_blank">Learn More</a><br>
  + Make sure you have the Nano app installed, then connect your ledger device via USB (Chrome/Opera only). <a href="https://link.medium.com/RbsZvsEkG7" target="_blank">Learn More</a><br>
  <br>
  </p>
  <div *ngIf="ledger.status === ledgerStatus.NOT_CONNECTED" class="uk-alert uk-alert-warning">
  