Improve reduce() tests

`0` has been removed as the first element of the `reduce` tests. Starting with `1` is a better choice since it will catch errors in the starting loop index. Example:

``` Javascript
var acc = this[0];       // Element 0 used
for (var i = 0; i < this.length; i++) {
  // First iteration will use element 0 again!
  acc = f(acc, this[i]);
```