[youtube_player_iframe] fix(PlayerState): cannot pause video

[chungxon]

While developing my app, I found that I can't pause the video when using the youtube_player_iframe package

After debugging, I found that getPlayerState returns the string "1.0". But in the PlayerState enum, you define the code value as int type, so this function always returns PlayerState.unknown. Please check the debug screenshot below, thank you