utils.general comment updates/bug fixes

detect.py

@@ -138,7 +138,7 @@ def detect(save_img=False):
 
     if save_txt or save_img:
         print('Results saved to %s' % Path(out))
-        if platform == 'darwin' and not opt.update:  # MacOS
+        if platform.system() == 'Darwin' and not opt.update:  # MacOS
             os.system('open ' + save_path)
 
     print('Done. (%.3fs)' % (time.time() - t0))