Fix Style/StringConcatenation RuboCop offense

Fix instances of: https://docs.rubocop.org/rubocop/cops_style.html#stylestringconcatenation in this project.

• Before: https://docs.gitlab.com/ee/user/application_security/dependency_list/
• After: http://eread-fix-string-concatenation-rubocop-offense.35.193.151.162.nip.io/ee/user/application_security/dependency_list/