Fix typo

src/howler.core.js

@@ -1251,7 +1251,7 @@
     },
 
     /**
-     * Fade a currently playing sound between two volumes (if no id is passsed, all sounds will fade).
+     * Fade a currently playing sound between two volumes (if no id is passed, all sounds will fade).
      * @param  {Number} from The value to fade from (0.0 to 1.0).
      * @param  {Number} to   The volume to fade to (0.0 to 1.0).
      * @param  {Number} len  Time in milliseconds to fade.