improve isArray check

* more correct
* when `Array.isArray` is available its a nice performance boost.
* toString approach is unfortunately slower then the instanceof approach

given:

```js
sequence(compose(
  cat,
  map(square),
  filter(odd),
  take(20)
), range(0, 1000)
);
```

the improvement in node 0.11.14 was from about 425,000 op/s to 515,000 op/s 
```
 v8: '3.26.33'
 node: '0.11.14'
```