docs: Use the new floating ment on skpaint.md

Screenshot:
  https://screenshot.googleplex.com/C3E0hpuNwdu.png
  https://screenshot.googleplex.com/vdfQMRc24Nv.png

BUG=skia:

NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=5757

Change-Id: I00b1bb01cab05592d19f020f3190576bf7907aa2
Reviewed-on: https://skia-review.googlesource.com/5757
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
2 files changed