feat(lib/*.js): change map-stream to through2

* update through2 to ^0.5.1
That's a officail note, it should be added to document when use this.

```
gulp.src('source-file')
  .pipe(gulp.dest('dest'))
  .on('end', cb)
  .resume();
```

Or listem `data` event to fix it

```
return through2.obj(saveFile)
  .on('data', function(){});
```