Added .ruby-gemset
Fixed failing test in about_asserts.rb

* Learned that the assert method is looking for some value which is truth-y

[#65851738]
Fixed failing test in about_assert.rb

* Learned that the assert method asks  if the argument is true or not.
* Learned that the method has an optional argument, a message to help
us figure out why the test is failing.

[#65851738]
Fixed the method test_assert_equality

[#65851738]
Fixed the test_a_better_way_of_asserting_equality test

* Learned about assert_equal method

[#65851738]
Completed all fixes in about_assert.rb

* Learned that there are some ways of asserting, and there're
better ways to do the same.

[#65851738]
Fixed all tests in about_nil.rb

- Learned that nil is an object.
- Learned that calling a method that nil doesn't know about
  would return NoMethodError with "undefined method" message.
  Learned that nil has several methods: #nil?, #to_s, #inspect.

[#65851740]
Accidentally unstaged a wrong file.