Refactor methods

Addressed each of your comments:
1. Fixed indentation to 2 spaces
2. Fixed nested 'each' blocks in lib/code_list.rb (discovered repeated_permutation)
3. Refactored update_list method in lib/code_list.rb
4. Refactored count_white_pegs method in lib/code_list.rb 
5. Refactored check_guess method in lib/guess_checker.rb