[canvaskit] Fix typo in docs example

Change-Id: Ie3b9ad724fa0d71ad1f433324cfcb76c769bfebe
No-Try: true
Docs-Preview: https://skia.org/?cl=350837
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350837
Reviewed-by: Kevin Lubick <kjlubick@google.com>
1 file changed