Update rubocop to disable a cop relevant only to rails 5
Update rubocop to disable a cop relevant only to rails 5

- References bbatsov/rubocop#3629

cysjonathan/coursemology2,Coursemology/coursemology2,Coursemology/coursemology2,Coursemology/coursemology2,Coursemology/coursemology2,cysjonathan/coursemology2,Coursemology/coursemology2,cysjonathan/coursemology2,Coursemology/coursemology2,Coursemology/coursemology2