Add trailing comma

Issue #7

Author: pilafmon

spec/mocha.spec.js

@@ -131,7 +131,7 @@ describe('The gulp-w3c-html-validator reporter()', () => {
          path:     'spec/html/valid.html',
          cwd:      'spec/',
          base:     'spec/html/',
-         contents: readFileSync('spec/html/valid.html')
+         contents: readFileSync('spec/html/valid.html'),
          };
       const mockFile = new Vinyl(vinylOptions);
       const stream = htmlValidator.reporter();