BugFix: the part of generating config obj

* ensure to be override config values even if type of value is boolean

lib/models/config.js

@@ -110,7 +110,7 @@ module.exports = function(crowi) {
       defaultConfig[ns] = {};
     }
     Object.keys(config[ns] || {}).forEach(function (key) {
-      if (config[ns][key]) {
+      if (config[ns][key] !== undefined) {
         defaultConfig[key] = config[ns][key];
       }
     });