Update release notes for 1.2.1
Update release notes for 1.2.1

laurenrother/riak,DavidAlphaFox/riak,yangchengjian/riak,authbox-lib/riak,amyvmiwei/riak,glickbot/riak,xuejianhai/riak,GabrielNicolasAvellaneda/riak,basho/riak,elkingtonmcb/riak,biddyweb/riak