Invoke IO.popen correctly for Ruby 1.9.3

Before this change, tests in gitlab_projects_spec were passing on Ruby
2.0.0 but not on 1.9.3.

spec/gitlab_projects_spec.rb

@@ -332,6 +332,6 @@ describe GitlabProjects do
   end
 
   def capture_in_tmp_repo(cmd)
-    IO.popen(cmd, chdir: tmp_repo_path).read.strip
+    IO.popen([*cmd, {chdir: tmp_repo_path}]).read.strip
   end
 end