Fixed inconsistency in quotes

docs/manual/en/buildTools/Testing-with-NPM.html

@@ -153,7 +153,7 @@ $ npm install three --save-dev
 					the three.js object is available and working. Create test/verify-three.js containing:
 <code>
 var THREE = require('three');
-var assert = require("assert");
+var assert = require('assert');
 
 describe('The THREE object', function() {
   it('should have a defined BasicShadowMap constant', function() {