[@types/youtube-player] Fix requiring playlist

This option of `Options.playerVars` are not required.
https://developers.google.com/youtube/player_parameters?playerVersion=HTML5#playlist

types/youtube-player/dist/types.d.ts

@@ -26,7 +26,7 @@ export interface Options {
         loop?: 0 | 1,
         modestbranding?: 1,
         origin?: string,
-        playlist: string,
+        playlist?: string,
         playsinline?: 0 | 1,
         rel?: 0 | 1,
         start?: number,