1. The cleanest way seems to be using the url() helper:
    {{ url()->previous() }}

2. URL::previous() works for me in my Laravel 5.1 project. Here is Laravel 5.1 
  doc for previous() method, which is accessible through URL Facade.

3. You can still try alternatives, in your views you can do:

    {{ redirect()->getUrlGenerator()->previous() }}
                        OR
    {{ redirect()->back()->getTargetUrl() }}