refactor(ShareButton): Reduced amount of changes to simplify review

Author: Kashuab

src/ShareButton.tsx

@@ -92,7 +92,7 @@ interface CustomProps<LinkOptions> {
    *  Takes a function that returns a Promise to be fulfilled before calling
    * `onClick`. If you do not return promise, `onClick` is called immediately.
    */
-  beforeOnClick?: () => void | Promise<void>;
+  beforeOnClick?: () => Promise<void> | void;
 
   /**
    * Takes a function to be called after closing share dialog.
@@ -133,7 +133,7 @@ export default class ShareButton<LinkOptions> extends Component<Props<LinkOption
     windowOpen(link, windowConfig, onShareWindowClose);
   };
 
-  handleClick = async (event: React.MouseEvent<HTMLButtonElement>): Promise<void> => {
+  handleClick = async (event: React.MouseEvent<HTMLButtonElement>) => {
     const {
       beforeOnClick,
       disabled,