Rebaseline fast/encoding/api/ascii-supersets.html.

An ICU roll (Chromium #293034) fixed an issue.

TBR=jshin@chromium.org
BUG=277062

Review URL: https://codereview.chromium.org/535793003

git-svn-id: svn://svn.chromium.org/blink/trunk@181276 bbb929c8-8fbe-4397-9dbb-9b2b20218538