Upgrade bleach to fix dodgy html5lib version
Upgrade bleach to fix dodgy html5lib version

Bleach 1.4.2 installs html5lib version 0.999 or greater.

This was fine, until version 0.999999999 (nine nines was released, which
doesn’t work.

Bleach 1.4.3 pins html5lib to 0.9999999 (seven nines), which stops the
bad version getting installed.
alphagov/notifications-api,alphagov/notifications-api