cmd/cgo: fix comment grammar
cmd/cgo: fix comment grammar

Change-Id: I9c881943685177ce14841da53ccaed301c4955dd
Reviewed-on: https://go-review.googlesource.com/c/149859
Reviewed-by: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>

CAFxX/go,golang/go,cloudflare/go,josharian/go,akutz/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,akutz/go,nawawi/go,nawawi/go,akutz/go,cloudflare/go,golang/go,CAFxX/go,akutz/go,CAFxX/go,josharian/go,CAFxX/go,cloudflare/go,nawawi/go,josharian/go,CAFxX/go,nawawi/go,josharian/go,golang/go,golang/go,golang/go,josharian/go,josharian/go,akutz/go,cloudflare/go,CAFxX/go,CAFxX/go,akutz/go,akutz/go,josharian/go,nawawi/go,josharian/go