Fix ScriptExtensions for 5 characters

Cherry pick upstream fix for
  http://bugs.icu-project.org/trac/ticket/13462
which is
  http://bugs.icu-project.org/trac/changeset/40667

TBR=mathias@chromium.org

Bug: v8:4743
Test: v8: test262/built-ins/RegExp/property-escapes/generated/*
Change-Id: I3f94b6bf519bd395bec1f73e5f8d602f93910032
Reviewed-on: https://chromium-review.googlesource.com/760120
Reviewed-by: Jungshik Shin <jshin@chromium.org>
4 files changed