fixed errors in about_nil.rb

* pivotal tracker id [#75411400]
* learned that nil has a few methods, such as .nil? and .inspect
Merge pull request #2 from glassbead0/75411400_about_nil_master

fixed errors in about_nil.rb

[Delivers #75411400]
Update about_objects.rb
Update about_objects.rb
Update about_objects.rb
Update about_objects.rb