minor correction to #35d235a7

minor correction to #35d235a7

code expects a single commit, not an array

diff --git a/lib/discourse_code_review/github_repo.rb b/lib/discourse_code_review/github_repo.rb
index 7cf4602..6674609 100644
--- a/lib/discourse_code_review/github_repo.rb
+++ b/lib/discourse_code_review/github_repo.rb
@@ -99,7 +99,7 @@ module DiscourseCodeReview
       git("pull")
       begin
         git("log -1 #{hash}", warn: false)
-        commits_since(hash, single: true, pull: false)
+        commits_since(hash, single: true, pull: false).first
       rescue StandardError
         nil
       end

GitHub sha: 52e1bab8