fix mistake, anonymous functions are not closures if there are no free v...

...ariables
In PHP, all anon functions (i.e. those that are created by {{function ()}} construct) use Closure class and so may be referred to as "closures". In strictly technical sense anon function that does not use any free variables (or {{$this}}) may be seen as a closure with empty context. So this distinction would be misleading here I think.