message: Update observer.md
  * Update observer.md
  migrate to 7.
  * Update observer.md
  * docs: docs_app/content/guide/observer.md
  * docs: docs_app/content/guide/observer.md
diff: @@ -20,7 +20,7 @@ observable.subscribe(observer);
  Observers in RxJS may also be *partial*. If you don't provide one of the callbacks, the execution of the Observable will still happen normally, except some types of notifications will be ignored, because they don't have a corresponding callback in the Observer.
  -The example below is an Observer without the `complete` callback:
  +The example below is an `Observer` without the `complete` callback:
  ```ts
  const observer = {
  @@ -29,18 +29,10 @@ const observer = {
  };
  ```
  -When subscribing to an Observable, you may also just provide the callbacks as arguments, without being attached to an Observer object, for instance like this:
  +When subscribing to an `Observable`, you may also just provide the next callback as an argument, without being attached to an `Observer` object, for instance like this:
  ```ts
  observable.subscribe(x => console.log('Observer got a next value: ' + x));
  ```
  -Internally in `observable.subscribe`, it will create an Observer object using the first callback argument as the `next` handler. All three types of callbacks may be provided as arguments:
  -
  -```ts
  -observable.subscribe(
  - x => console.log('Observer got a next value: ' + x),
  - err => console.error('Observer got an error: ' + err),
  - () => console.log('Observer got a complete notification')
  -);
  -```
  +Internally in `observable.subscribe`, it will create an `Observer` object using the callback argument as the `next` handler.
  