doc: s/race/ethnicity/ in the Code of Conduct
doc: s/race/ethnicity/ in the Code of Conduct

As agreed upon by the Code of Conduct working group, "race" may refer to
an attempt to classify people based on "defining characteristics",
regardless of how this people view themselves, while "ethnicity" refers
to how people identify themselves.

The Code of Conduct working group believes that the term "ethnicity"
will be more comprehensive and inclusive, and will better serve the Go
community.

Change-Id: I724b72cadb8cf29b4bac8f83017b0303feae3c94
Reviewed-on: https://go-review.googlesource.com/32133
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

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