downgrade rake again
downgrade rake again

it must have accidentally be gotten updated via #390

rubocops Gemfile suggests gem 'rake', '~> 12.0' at this
point in time so we can safely stick to 12.0.0

https://github.com/bbatsov/rubocop/blob/082408/Gemfile#L9

Signed-off-by: Maximilian Meister <d082c6e85b1479677ce48cb91ac104a594c00930@suse.de>

kubic-project/velum,vitoravelino/velum,MaximilianMeister/velum,kubic-project/velum,vitoravelino/velum,MaximilianMeister/velum,kubic-project/velum,MaximilianMeister/velum,kubic-project/velum,MaximilianMeister/velum,ereslibre/velum,ereslibre/velum,ereslibre/velum,ereslibre/velum,vitoravelino/velum,vitoravelino/velum