errgroup: fix misleading comment in MD5All example
errgroup: fix misleading comment in MD5All example

Change-Id: I0c2f0ce9b6006dac13c5f5faed752a2475992805
Reviewed-on: https://go-review.googlesource.com/33851
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/sync