Fixed about_hashes.rb to pass all tests

Learned about:
- creating hashes

[#65851750]
Fixed about_hashes.rb to pass all tests

Learned about:
- hash literals,
- various ways to access and modify values in hashes,

[#65851750]
Fixed about_hashes.rb to pass all tests

Learned about:
- testing equality of hashes

[#65851750]
Fixed about_hashes.rb to pass all tests

Learned about:
- testing hash keys,

[#65851750]
Fixed about_hashes.rb to pass all tests

Learned about:
- combining hashes,
- default values when creating a new hash,
- that a block can be passed as a default value for new hash.

[#65851750]