Update walkers.php

All start_lvl and end_lvl functions were causeing the following erros. Updated the functions parameters to match the parent functions.

Declaration of Side_Menu_Walker::start_lvl() should be compatible with Walker::start_lvl(&$output, $depth = 0, $args = Array) on line 371 in file /home/easymoda/public_html/wp-content/themes/reactor/library/inc/extensions/walkers.php
Merge pull request #19 from danieliser/patch-1

Update walkers.php