Fix BasicObject#instance_eval signature

[hanachin]

irb(main):001:0> 42.instance_eval { p _1 }
42
=> 42
irb(main):002:-> 42.instance_eval(&->{})
Traceback (most recent call last):
        6: from /usr/local/var/rbenv/versions/master/bin/irb:23:in `<main>'
        5: from /usr/local/var/rbenv/versions/master/bin/irb:23:in `load'
        4: from /usr/local/var/rbenv/versions/master/lib/ruby/gems/2.7.0/gems/irb-1.1.0.pre.3/exe/irb:11:in `<top (required)>'
        3: from (irb):2
        2: from (irb):2:in `instance_eval'
        1: from (irb):2:in `block in irb_binding'
ArgumentError (wrong number of arguments (given 1, expected 0))

[soutaro]

I will check what is happening...

[soutaro]

Okay, it is because BasicObject does not provide some important methods like method, class, or singleton_class. I think skip writing tests for BasicObject would make sense.

[hanachin]

#41 made BasicObject testable 👏 so I added a test ✌️