no using underscore -> no last() on collection.

This is the reason why adding the 2nd item on collection doesnt work. solution simple last function has been  added.
```js
last: function () {
	return this.length > 0 ? this.at(this.length - 1) : null;
}
```

I actually don't really understand the comment. If it's only me (@passy? @sindresorhus?), then nevermind. Either way, they should look like the others:

```js
//(space)(Capital) full sentences. Max 80-char length before new line.
```

:)