Fix preloading

Preload players were unmounting and remounting when media is loaded later, which doesn't play the media until browser refocus (which ruins the whole point of preloading)
Using an array (together with the `key` for each player) means the same player is used when something is loaded later

src/ReactPlayer.js

@@ -154,8 +154,7 @@ export default class ReactPlayer extends Component {
     const preloadPlayers = this.renderPreloadPlayers(url)
     return (
       <div ref={this.wrapperRef} style={{ ...style, width, height }} {...otherProps}>
-        {activePlayer}
-        {preloadPlayers}
+        {[ activePlayer, ...preloadPlayers ]}
       </div>
     )
   }