Go 1.6 is soon (but not yet).

Fixes #14301.

Change-Id: I85e329b643adcb5d4fa680c5333fbc1f928d4d9d
Reviewed-on: https://go-review.googlesource.com/19550Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>