Converted method to proc is given wrong number arguments

To reproduce:

```ruby
def register(a, b)
end

{
  1 => 'a',
  2 => 'b'
}.map(&method(:register))

```

Error:

```
pocus.rb:1:in `register': wrong number of arguments (given 1, expected 2) (ArgumentError)
	from pocus.rb:1:in `register'
	from pocus.rb:6:in `map'
	from pocus.rb:6:in `<main>'
```