Change two-review rule to one (#1802)
Change two-review rule to one (#1802)

Two are encouraged but no longer mandatory.
sophie-h/boulder,bmw/boulder,ZCloud-Firstserver/boulder,lucasallan/boulder,letsencrypt/boulder,jcjones/boulder,jfrazelle/boulder,letsencrypt/boulder,jcjones/boulder,ZCloud-Firstserver/boulder,bmw/boulder,jsha/boulder,jcjones/boulder,benileo/boulder,jsha/boulder,benileo/boulder,ZCloud-Firstserver/boulder,ibukanov/boulder,benileo/boulder,lucasallan/boulder,benileo/boulder,jfrazelle/boulder,jfrazelle/boulder,sophie-h/boulder,jfrazelle/boulder,ZCloud-Firstserver/boulder,jsha/boulder,ibukanov/boulder,letsencrypt/boulder,sophie-h/boulder,lucasallan/boulder,bmw/boulder,ibukanov/boulder,jcjones/boulder