Merge pull request opencv#19291 from gpiffault:docs-js_usage-fix_imshow

Author: alalek

doc/js_tutorials/js_setup/js_usage/js_usage.markdown

@@ -82,7 +82,7 @@ In this tutorial, we just show a cv.Mat on screen. To show a cv.Mat, you need a
 
 You can use cv.imshow to show cv.Mat on the canvas.
 @code{.js}
-cv.imshow(mat, "outputCanvas");
+cv.imshow("outputCanvas", mat);
 @endcode
 
 Putting all of the steps together, the final index.html is shown below.