message: docs(groupBy): fix examples
  Fixes a few glitches so the examples are runnable.
  This also includes stripping the type definitions since the example
  code blocks specify `javascript`, and the other examples I've seen so
  far don't seem to include these.
diff: @@ -38,12 +38,7 @@ export function groupBy<T, K, R>(keySelector: (value: T) => K, elementSelector?:
  * import { of } from 'rxjs';
  * import { mergeMap, groupBy, reduce } from 'rxjs/operators';
  *
  - * interface Obj {
  - * id: number,
  - * name: string,
  - * }
  - *
  - * of<Obj>(
  + * of(
  * {id: 1, name: 'JavaScript'},
  * {id: 2, name: 'Parcel'},
  * {id: 2, name: 'webpack'},
  @@ -69,18 +64,21 @@ export function groupBy<T, K, R>(keySelector: (value: T) => K, elementSelector?:
  *
  * ```javascript
  * import { of } from 'rxjs';
  - * import { mergeMap, groupBy, map, reduce } from 'rxjs/operators';
  + * import { groupBy, map, mergeMap, reduce } from 'rxjs/operators';
  *
  - * of<Obj>(
  + * of(
  * { id: 1, name: 'JavaScript' },
  * { id: 2, name: 'Parcel' },
  * { id: 2, name: 'webpack' },
  - * {id: 1, name: 'TypeScript'}
  + * { id: 1, name: 'TypeScript' },
  * { id: 3, name: 'TSLint' }
  - * ).pipe(
  + * )
  + * .pipe(
  * groupBy(p => p.id, p => p.name),
  - * mergeMap( (group$) => group$.pipe(reduce((acc, cur) => [...acc, cur], ["" + group$.key]))),
  - * map(arr => ({'id': parseInt(arr[0]), 'values': arr.slice(1)})),
  + * mergeMap(group$ =>
  + * group$.pipe(reduce((acc, cur) => [...acc, cur], [`${group$.key}`]))
  + * ),
  + * map(arr => ({ id: parseInt(arr[0], 10), values: arr.slice(1) }))
  * )
  * .subscribe(p => console.log(p));
  *
  