codereview: switch defaultcc to golang-codereviews
codereview: switch defaultcc to golang-codereviews

See this thread for background:
https://groups.google.com/forum/#!topic/golang-dev/xG7vPi21r8g

R=golang-codereviews, r, iant
CC=golang-codereviews
https://codereview.appspot.com/44290045

polydawn-ports/go.net,fernandez14/go.net,ssor/go.net