Improve test code (#142)

* Fix node module name.

* Unnecessary require "should".

Author: ryoichi-obara

docs/creating-nodes/first-node.md

@@ -190,8 +190,7 @@ Using this framework, you can create test flows, and then assert that your node
 <h4 id="lower-casespecjs"><i class="fa fa-file-o"></i> test/lower-case_spec.js</h4>
 
 ```javascript
-var should = require("should");
-var helper = require("node-red-test-helper");
+var helper = require("node-red-node-test-helper");
 var lowerNode = require("../lower-case.js");
 
 describe('lower-case Node', function () {