Made changes to about_nil.rb to make it work

* Learned nil is a full object

* Not sure about how exceptions work, but made the koan work.

* Learned that there is a test to object ".nil?" that will return true only if object is nill

* Learned nil.to_s returns the empty string, which makes sense

* Learned nil.inspect returns "nil", but I am not sure what inspect is supposed to do yet.

[#65851496]