Unicorn will not start after upgrading to 7.9.0 on source installation

I get the following stderr log message when trying to start GitLab after the update (unicorn doesn't start).

I, [2015-03-23T16:05:46.815950 #6883]  INFO -- : Refreshing Gem list
/home/git/gitlab/vendor/bundle/ruby/2.0.0/gems/activesupport-4.1.9/lib/active_support/dependencies.rb:247:in `require': /home/git/gitlab/vendor/bundle/ruby/2.0.0/gems/gemnasium-gitlab-service-0.2.5/lib/gemnasium/gitlab_service/client.rb:17: syntax error, unexpected ',' (SyntaxError)
...oad_files(files, project_slug:, branch_name:, commit_sha:)

Here's the console output:

$ 
$ sudo service gitlab start
Removing stale Sidekiq job dispatcher pid. This is most likely caused by Sidekiq crashing the last time it ran.
Starting both the GitLab Unicorn and Sidekiqmaster failed to start, check stderr log for details
.
The GitLab Unicorn web server is not running.
The GitLab Sidekiq job dispatcher with pid 7380 is running.
$