Rubocop not running in Ruby code

I noticed that Rubocop isn't failing and catching these mistakes:

$ bundle exec rubocop lib/gitlab//git/gitlab_projects.rb
Inspecting 1 file
W

Offenses:

lib/gitlab/git/gitlab_projects.rb:44:1: C: Layout/EmptyLines: Extra blank line detected.
lib/gitlab/git/gitlab_projects.rb:45:7: C: Layout/EmptyLineBetweenDefs: Use empty lines between method definitions.
      def shard_name
      ^^^
lib/gitlab/git/gitlab_projects.rb:45:7: W: Lint/DuplicateMethods: Method Gitlab::Git::GitlabProjects#shard_name is defined at both lib/gitlab/git/gitlab_projects.rb:11 and lib/gitlab/git/gitlab_projects.rb:45.
      def shard_name
      ^^^
lib/gitlab/git/gitlab_projects.rb:49:7: C: Style/TrivialAccessors: Use attr_reader to define trivial reader methods.
      def shard_path
      ^^^
lib/gitlab/git/gitlab_projects.rb:69:7: W: Lint/DuplicateMethods: Method Gitlab::Git::GitlabProjects#shard_path is defined at both lib/gitlab/git/gitlab_projects.rb:49 and lib/gitlab/git/gitlab_projects.rb:69.
      def shard_path
      ^^^
<snip>