ResourceLoaderEditToolbarModule: Fix PHP Strict Standards warning

PHP Strict Standards:  Declaration of ResourceLoaderEditToolbarModule::getLessCompiler()
should be compatible with ResourceLoaderFileModule::getLessCompiler(ResourceLoaderContext $context = NULL)
in …/includes/resourceloader/ResourceLoaderEditToolbarModule.php on line 0

Change-Id: I6b2de82028a81db7c65eb22f2535fbe4fa70cc91