a trivial bug

[niunuinui]

i think line 215 should be

 warning(['only %d checkerboards found.\n',...
        '10 images is the minimum number of boards recommended for an accurate calibration (though more is better, orignal calibration used 50+)\n',...
        'Check your images and keep in mind, lighting, occlusions and backgrounds with roughly checkered patterns'], sum(imagesUsed));