Use Ci::Pipeline#latest for finding pipelines

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7333#note_18861407

lib/gitlab/badge/build/status.rb

@@ -20,7 +20,8 @@ module Gitlab
 
         def status
           @project.pipelines
-            .where(sha: @sha, ref: @ref)
+            .where(sha: @sha)
+            .latest(@ref)
             .status || 'unknown'
         end
 

spec/lib/gitlab/badge/build/status_spec.rb

@@ -69,8 +69,8 @@ describe Gitlab::Badge::Build::Status do
         new_build.success!
       end
 
-      it 'reports the compound status' do
-        expect(badge.status).to eq 'failed'
+      it 'does not take outdated pipeline into account' do
+        expect(badge.status).to eq 'success'
       end
     end
   end