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, gobot, golang-dev, dsymonds
CC=golang-codereviews, golang-dev
https://codereview.appspot.com/44450043

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