• Breaking change: stellar-sdk no longer ships with an EventSource
  polyfill. If you plan to support IE11 / Edge, please use
  event-source-polyfill
  to set window.EventSource.
• Upgrade stellar-base to a version that doesn't use the crypto library,
  fixing a bug with Angular 6
• Add Server.prototype.fetchTimebounds, a helper function that helps you set
  the timebounds property when initting TransactionBuilder. It bases the
  timebounds on server time rather than local time.