code: function(hook, rules) {
  			if (cfg.AVAILABLE_HOOKS.indexOf(hook) < 0 && !this.ignore) {
  				this.error('hook "' + hook + '" not support');
  			}
  
  			if (!hooks[hook]) {
  				hooks[hook] = new Githook(rules);
  			}
  			return hooks[hook];
  		}
docs: add a new hook
  @param  {String} hook  [hook name]
  @param  {Object} rules [hook trigger rules]
  @return Githook