Changed column title (to improve translations)

I think it's more accurate and give a bit more context.

system/author/settings/userlist.twig

@@ -17,7 +17,7 @@
 						<li class="col username">{{ __('Username') }}</li><li 
 							class="col userrole">{{ __('Role') }}</li><li 
 							class="col email">{{ __('E-Mail') }}</li><li 
-							class="col edit">{{ __('Edit') }}</li>
+							class="col edit">{{ __('Action') }}</li>
 					</ul>
 				</li>
 				{% for user in userdata %}