[patch] use forwardRef instead of ref (#97)

- this stops a warning being produced when testing which reads:
> Warning: Function components cannot be given refs. Attempts to access this ref will fail. Did you mean to use React.forwardRef()?
 - Fixes #67

Author: TimLehner

src/hoc/trackWindowScroll.js

@@ -124,7 +124,7 @@ const trackWindowScroll = BaseComponent => {
 
 			return (
 				<BaseComponent
-					ref={this.baseComponentRef}
+					forwardRef={this.baseComponentRef}
 					scrollPosition={scrollPosition}
 					{...props}
 				/>