Use correct type for rc-tooltip's overlay (#18579)

The previous type signature doesn't allow e.g. strings to be passed in,
even though they're completely valid.

types/rc-tooltip/index.d.ts

@@ -1,6 +1,7 @@
 // Type definitions for rc-tooltip v3.4.2
 // Project: https://github.com/react-component/tooltip
 // Definitions by: rhysd <https://rhysd.github.io>
+//                 ahstro <http://ahst.ro>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -26,7 +27,7 @@ declare namespace Tooltip {
 		placement?: Placement | Object;
 		align?: Object;
 		onPopupAlign?: (popupDomNode: Element, align: Object) => void;
-		overlay: React.ReactElement<any> | (() => React.ReactElement<any>);
+		overlay: React.ReactNode;
 		arrowContent?: React.ReactNode;
 		getTooltipContainer?: () => Element;
 		destroyTooltipOnHide?: boolean;

types/rc-tooltip/rc-tooltip-tests.tsx

@@ -9,6 +9,13 @@ ReactDOM.render(
     document.querySelector('.app')
 );
 
+ReactDOM.render(
+    <Tooltip overlay="tooltip">
+        <a href='#'>hover</a>
+    </Tooltip>,
+    document.querySelector('.app')
+);
+
 ReactDOM.render(
     <Tooltip
         placement="bottomRight"