Describe the bug
i noticed the bug that when we lock the joystick on Y axis it still return angle so i think it will be good if it not return angle from x axis when its locked on Y.

To Reproduce
Steps to reproduce the behavior:

1. download : https://github.com/yoannmoinet/nipplejs/blob/master/example/dual-joysticks.html
2. Lock the 2nd joystick on Y
3. move the mouse towards X axis
4. you will see that angle is displayed of axis too although UI is locked on Y

screenshot :

Desktop (please complete the following information):

• OS: windows 7
• Browser chrome
• Version latest