Merge pull request #6 from kevinrambaud/master

Fix incomplete function declaration for appError

sections/errorhandling/useonlythebuiltinerror.md

@@ -42,13 +42,15 @@ if(!productToAdd)
 
 ```javascript
 //centralized error object that derives from Node’s Error
-function name, httpCode, description, isOperational) {
+function appError(name, httpCode, description, isOperational) {
     Error.call(this);
     Error.captureStackTrace(this);
     this.name = name;
     //...other properties assigned here
 };
+
 appError.prototype.__proto__ = Error.prototype;
+
 module.exports.appError = appError;
  
 //client throwing an exception