Fix markdown typo in the style guide

Change-Id: I58a67d145ee088142c2791f7b447beaaf93aef56
No-Try: true
Docs-Preview: https://skia.org/?cl=292496
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292496
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
1 file changed