Joystick appears invisible when immediately cloned from the repository

[denesh-globotix]

Thank you for such a wonderful wrapper for nipplejs. I am used to working with this library in typical html and it's great to be able to use the same set of features with ReactJS. Would just like to point out that when I first cloned the package the color field was missing from the example snippet provided in the README.md and so the joystick appeared invisible. This is likely due to the color field not being set.

Adding the color field into options fixes this.

          options={{ 
            mode: 'static', 
            position: { top: '50%', left: '50%' }, 
            color: 'red',
          }}

Thanks once again for this package!