[@storybook/react] Array support for RenderFunction (#22529)

* Update storybook__react-tests.tsx

* Array support for RenderFunction

Follows React v16 update

* fix Jenkins build error

* fix tests error

types/storybook__react/index.d.ts

@@ -1,6 +1,7 @@
 // Type definitions for @storybook/react 3.0
 // Project: https://github.com/storybooks/storybook
 // Definitions by: Joscha Feth <https://github.com/joscha>
+//                 Anton Izmailov <https://github.com/wapgear>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -9,7 +10,7 @@
 import * as React from 'react';
 
 export type Renderable = React.ComponentType | JSX.Element;
-export type RenderFunction = () => Renderable;
+export type RenderFunction = () => Renderable | Renderable[];
 
 export type StoryDecorator = (story: RenderFunction, context: { kind: string, story: string }) => Renderable | null;
 

types/storybook__react/storybook__react-tests.tsx

@@ -6,7 +6,8 @@ const Decorator = (story: RenderFunction) => <div>{story()}</div>;
 storiesOf('Welcome', module)
     // local addDecorator
     .addDecorator(Decorator)
-    .add('to Storybook', () => <div/>);
+    .add('to Storybook', () => <div/>)
+    .add('to Storybook as Array', () => [<div />, <div />]);
 
 // global addDecorator
 addDecorator(Decorator);
@@ -26,6 +27,7 @@ storiesOf<AnyAddon>('withAnyAddon', module)
     .addWithSideEffect('custom story', () => <div/>)
     .addWithSideEffect('more', () => <div/>)
     .add('another story', () => <div/>)
+    .add('to Storybook as Array', () => [<div />, <div />])
     .addWithSideEffect('even more', () => <div/>);
 
 // configure