code: function base64tpjpg(base64ImageData, filename) {
      var promise = new Promise(function(resolve, reject) {
          var base64Data = base64ImageData.replace(/^data:image\/\w+;base64,/, "");
          var dataBuffer = new Buffer(base64Data, 'base64');
          fs.writeFile(tmpimage, dataBuffer, function(err) {
              if (err) {
                  reject(err);
              } else {
                  execFile(mozjpeg, ['-outfile', filename, tmpimage], function(err) {
                      if (err) {
                          reject(err);
                      } else {
                          fs.unlink(tmpimage, function(err) {
                              resolve(filename);
                          });
                      }
                  });
              }
          });
      });
      return promise;
  }
docs: base64Image字串 轉 jpg
  @param  {String} base64ImageData image src中的字串
  @param  {String} filename        路徑與檔名，需要以.jpg結尾
  @return {Promise}                Promise