Merge branch 'viewer' into 'master'

update viewer api

See merge request CBCTF/bullseye-web!63

Author: m---

app/controllers/external_api/v1/viewer_controller.rb

@@ -138,6 +138,7 @@ def score
         problem_id: problem.id,
         name: problem.title,
         round_id: round&.id,
+        round_start_at: round&.start_at,
         ntrials: problem.ntrials,
         succeeded: score.succeeded,
         x11_required: problem.x11_required,