how to set framerate of gif (gifAnimation lib)?

the exported gif always running at 10 fps. how to make higher fps;
gifAnimation 3.0.0 _ processing 3.3.4

    import gifAnimation.*;
    GifMaker gifExport;
    float x;

    void setup() {
      size(200, 200);
      frameRate(30);
      gifExport = new GifMaker(this, "export.gif");
      gifExport.setRepeat(0);
    //setDelay()  can make gif slower ,but can't make gif run faster ,
      gifExport.setDelay(0);
    }
    void draw() {
      x=x+3;
      fill(250);
      ellipse(x,10,30,30);
      gifExport.addFrame();
    }

    void keyPressed() {
      gifExport.finish();
    }