Fix StringUtils on Xbox One
Fix StringUtils on Xbox One

Using the spread operator in StringUtils causes issues on Xbox One.
It has something to do with the compiler's polyfill for it.  But
there's no reason we have to use the spread operator instead of
Function.apply in this instance.

Closes #2186

Change-Id: If8b3ff436f852ccae1f1a8c3ee5b7d8c142e15cf

shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player