Fix current build arrow

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/27939

app/helpers/builds_helper.rb

 module BuildsHelper
   def sidebar_build_class(build, current_build)
     build_class = ''
-    build_class += ' active' if build == current_build
+    build_class += ' active' if build.id === current_build.id
     build_class += ' retried' if build.retried?
     build_class
   end

changelogs/unreleased/27939-fix-current-build-arrow.yml

+---
+title: Fix current build arrow indicator
+merge_request:
+author:

spec/features/projects/builds_spec.rb

@@ -109,6 +109,10 @@ feature 'Builds', :feature do
         expect(page).to have_content pipeline.git_commit_message
         expect(page).to have_content pipeline.git_author_name
       end
+
+      it 'shows active build' do
+        expect(page).to have_selector('.build-job.active')
+      end
     end
 
     context "Job from other project" do