[ES6] Different errors during parsing ordinary function and arrow function

[GSkachkov]

It seems that we have different error message in case of errors in parsing of the function parameters
>>> var arr = (a, ...last,)=> {return last;};
Unexpected token '...'
>>> var f = function (a, ...last,) {return last;};
Unexpected token ','. Rest parameter should be the last parameter in a function declaration.

[Caio Lima]

I think the report of ordinary functions more clear. I think we should give same syntax error to them.

I am interested  working in this =).