Fix Array#sample when pass count argument

When you pass `count` argument to Array#sample it returns first `count` elements always

```ruby
arr = [1, 2, 3, 4, 5]
arr.sample(3) # => [3, 1, 2]
arr.sample(3) # => [3, 1, 2]
arr.sample(3) # => [3, 1, 2]
```