Fix documentation example for getPlaylistTracks (#318)

Author: danguilherme

README.md

@@ -963,7 +963,7 @@ var spotifyApi = new SpotifyWebApi({
 
 // Get tracks in a playlist
 api
-  .getPlaylistTracks('thelinmichael', '3ktAYNcRHpazJ9qecm3ptn', {
+  .getPlaylistTracks('3ktAYNcRHpazJ9qecm3ptn', {
     offset: 1,
     limit: 5,
     fields: 'items'