Fixed about_to_str.rb to pass tests

 Learned that:
    * #to_s returns a string representation,
    * normally objects cannot be used where strings are expected,
    * #to_str also returns a string representation.

[#65851800]
Fixed about_to_str.rb to pass tests

 Learned that:
    * #to_str allows objects to be treated as strings,
    * user defined code can check for #to_str.

[#65851800]
Merge pull request #25 from mkreyman/65851800_about_to_str_master

about to str master

[Delivers #65851800]