Fix CanvasKit generated documentation to work with emscripten 1.39.16.

In https://skia-review.googlesource.com/c/skia/+/291182 emscripten was updated
to 1.39.16.  This introduced a breaking API change to the CanvasKit
initialization callback, which becomes simply `then()` as opposed to
`ready().then()`.  In the course of this change, I missed a few `ready()` calls,
which has broken the examples in public-facing documentation.
E.g. https://skia.org/user/modules/canvaskit.  This CL fixes that.

Bug: NONE
Change-Id: I857b4653747cffc3870bf92d479dc88c3fd7d64a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292097
Reviewed-by: Kevin Lubick <kjlubick@google.com>
4 files changed