message: docs(aio): add missing closing backtick
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diff: @@ -191,7 +191,7 @@ give it a `catchError()` operator.
  region="getHeroes-2" >
  </code-example>
  -The `catchError()` operator intercepts an **`Observable that failed**.
  +The `catchError()` operator intercepts an **`Observable` that failed**.
  It passes the error an _error handler_ that can do what it wants with the error.
  The following `handleError()` method reports the error and then returns an
  