Upgrade Rubocop version pin from 0.23.0 -> 0.24.1

This didn't result in any new lints.

Change-Id: I21d0d4b8f6f7afb4ed2a2ead6f6fe58fefe9abd3
Reviewed-on: http://gerrit.causes.com/40446
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>