old we.js is plugin function to check is one npm module is plugin
function oldIsPlugin (nodeModulePath) {
          // then check if the npm module is one plugin
          try {
            if (fs.statSync( path.resolve( nodeModulePath, 'plugin.js' ) )) {
              return true;
            } else {
              return false;
            }
          } catch (e) {
            return false;
          }
        }