Correct BackgroundJobs page for both OSX and linux

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/admin/background_jobs_controller.rb

 class Admin::BackgroundJobsController < Admin::ApplicationController
   def show
-    ps_output, _ = Gitlab::Popen.popen(%W(ps -U #{Settings.gitlab.user} -o euser,pid,pcpu,pmem,stat,start,command))
+    ps_output, _ = Gitlab::Popen.popen(%W(ps -U #{Settings.gitlab.user} -o pid,pcpu,pmem,stat,start,command))
     @sidekiq_processes = ps_output.split("\n").grep(/sidekiq/)
   end
 end