message: docs: correct the spelling mistake in observables error handling code
  This commit fixes a spelling error in the word error in the
  observables.md guide. It is currently
  spelled errror  and the mistake is not intentional.
  PR Close
diff: @@ -112,7 +112,7 @@ Because observables produce values asynchronously, try/catch will not effectivel
  <code-example>
  myObservable.subscribe({
  next(num) { console.log('Next num: ' + num)},
  - error(err) { console.log('Received an errror: ' + err)}
  + error(err) { console.log('Received an error: ' + err)}
  });
  </code-example>
  