code: function modulePath(module, node_modules) {
    var pkgFile = path.join(node_modules, module, 'package.json');
    if (!fs.existsSync(pkgFile)) {
      return null;
    }
    var data = fs.readFileSync(pkgFile, 'utf8');
    var pkg = JSON.parse(data);
    var fileName = pkg.main || 'index.js';
    var filePath = path.join(node_modules, module, fileName);
    return realRequirPath(filePath);
  }
docs: get required module full path
  
  @param module module
  @returns {*} /User/XXXX/node_modules/module/index.js