Removed double newline from output of migrate --list

refs [#23359](https://code.djangoproject.com/ticket/23359) and PR https://github.com/django/django/pull/3153#issuecomment-68471839
Tim pointed out to me that you are working on https://github.com/django/django/pull/3467 . I don't know if this interferes with #24068.

If your patch goes into 1.8 and makes the changes here and in #24068 obsolete, I'm not sure we even need to merge this patch and can close the ticket as duplicate.