Requre 01.rb in 01_spec.rb
Add --color option globally to .rspec
Reorder prime? cases
Use one-line if-statement
Eliminate return keyword from prime? method through reformulation of the condition
Eliminate self keyword from prime_factors
Use symbol to proc notation in map
Replace each with each_with_object
Remove validation from Array#average
Use &: notation in map method in Array#average
Replace each with each_with_object
Use Array#zip in combine_with