Fixes bug in Timeline.prototype.resolve() validation

resolve() isn't handling frame labels with a leading numeric correctly. If I created a label on frame 10 called "99RedBaloons" and then later do `gotoAndPlay("99RedBaloons");` this function would return 99 as opposed to 10. Casting the contents of `positionOrLabel` using Number() as opposed to parseFloat() will produce more consistent results.

For more on parseFloat vs Number, see https://stackoverflow.com/questions/12227594/which-is-better-numberx-or-parsefloatx