Fix spec to test behavior of Array#== with Float::NAN
Fix spec to test behavior of Array#== with Float::NAN

* Explain why it behaves that way in the description.
* See 9468751cb2db0cb88db210678481fd4ffb46e679.

eregon/rubyspec,ruby/spec,eregon/rubyspec,nobu/rubyspec,nobu/rubyspec,eregon/rubyspec,ruby/spec,ruby/spec,nobu/rubyspec