message: docs(tutorial_js_usage): fix imshow usage
diff: @@ -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.
  