Corrected issues identified by rubocop to ex11
Corrected issues identified by rubocop to ex12
Corrected issues identified by rubocop to ex14
Corrected issues identified by rubocop to ex15
Corrected issues identified by rubocop to ex16
Corrected issues identified by rubocop to ex17
Corrected issues identified by rubocop to ex18
Corrected issues identified by rubocop to ex19
Corrected issues identified by rubocop to ex20
Corrected issues identified by rubocop to ex21
Corrected issues identified by rubocop to ex24