doc/go1.11: clarify GOOS/GOARCH pair of WebAssembly port
doc/go1.11: clarify GOOS/GOARCH pair of WebAssembly port

It's more common to specify GOOS/GOARCH values in that order,
rather than the inverse. Fix the order.

Updates #18892.

Change-Id: I8551508599e019f6617dc007397b562c9926418d
Reviewed-on: https://go-review.googlesource.com/120057
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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