fix a problem for updating config cache

* update even if config value is 'false'

lib/models/config.js

@@ -62,7 +62,7 @@ module.exports = function(crowi) {
     var originalConfig = crowi.getConfig();
     var newNSConfig = originalConfig[ns] || {};
     Object.keys(config).forEach(function (key) {
-      if (config[key] || config[key] === '') {
+      if (config[key] || config[key] === '' || config[key] === false) {
         newNSConfig[key] = config[key];
       }
     });