message: updated node detection
diff: * DESC: Common test/demo slides for all library features
  * DEPS: Loaded by `pptxgenjs-demo.js` and `nodejs-demo.js`
  * VER.: 2.0.0
  -* REL.: 20180319
  +* REL.: 20180416
  */
  // Detect Node.js
  -var NODEJS = ( typeof module !== 'undefined' && module.exports );
  +var NODEJS = ( typeof module !== 'undefined' && module.exports && typeof require === 'function' && require('fs') );
  if (NODEJS) { var LOGO_STARLABS; }
  // Constants
  