Fixed track event utme issue where utme was prefixed by "null" causing events not to track correctly

Fixed tracking issue (on haxe 2.1 at least) where the utme was incorrectly built. The utme was built with null + event details. This prevented me from correctly updating sending analytics events event the correct event details were being included.

When/if this fix is merge could you please update the haxelib (2.1) so that the rest of the developers can get this fix. Thanks, Phil.