Fix comment to indicate function can return string if output argument provided
Fix comment to indicate function can return string if output argument provided

yasha0b1/robotics-toolbox-matlab,jaejunlee0538/robotics-toolbox-matlab,konradb3/robotics-toolbox-matlab,yasha0b1/robotics-toolbox-matlab,yasha0b1/robotics-toolbox-matlab,jaejunlee0538/robotics-toolbox-matlab,konradb3/robotics-toolbox-matlab,jaejunlee0538/robotics-toolbox-matlab,konradb3/robotics-toolbox-matlab,konradb3/robotics-toolbox-matlab,konradb3/robotics-toolbox-matlab,yasha0b1/robotics-toolbox-matlab,jaejunlee0538/robotics-toolbox-matlab,yasha0b1/robotics-toolbox-matlab,jaejunlee0538/robotics-toolbox-matlab