add config schema

lib/models/config.js

@@ -280,6 +280,11 @@ module.exports = function(crowi) {
     return getValueForCrowiNS(config, key);
   };
 
+   configSchema.statics.isEnabledPassportTwitter = function(config) {
+    const key = 'security:passport-twitter:isEnabled';
+    return getValueForCrowiNS(config, key);
+  };
+
   configSchema.statics.isSameUsernameTreatedAsIdenticalUser = function(config, providerType) {
     const key = `security:passport-${providerType}:isSameUsernameTreatedAsIdenticalUser`;
     return getValueForCrowiNS(config, key);