net/http/httputil: fix typo in ReverseProxy godoc
net/http/httputil: fix typo in ReverseProxy godoc

Change-Id: Iea33fe64403ca2e6f87a4e070af5e97d96506e41
Reviewed-on: https://go-review.googlesource.com/c/157118
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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