net/http: use keyed composite literal
net/http: use keyed composite literal

Makes vet happy.

Updates #11041

Change-Id: I23ca413c03ff387359440af8114786cd7880a048
Reviewed-on: https://go-review.googlesource.com/27124
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

josharian/go,linux-on-ibm-z/go,codestation/go,cloudflare/go,linux-on-ibm-z/go,ImJasonH/go,goodlang/good,josharian/go,CAFxX/go,codestation/go,nawawi/go,CAFxX/go,momchil-velikov/go,vsekhar/elastic-go,vsekhar/elastic-go,derekmarcotte/go,CAFxX/go,suncycheng/go,CAFxX/go,polyverse-security/go,ImJasonH/go,vsekhar/elastic-go,nawawi/go,nawawi/go,momchil-velikov/go,josharian/go,cloudflare/go,vsekhar/elastic-go,Cofyc/go,goodlang/good,suncycheng/go,nawawi/go,nawawi/go,linux-on-ibm-z/go,goodlang/good,ImJasonH/go,codestation/go,golang/go,polyverse-security/go,akutz/go,goodlang/good,Cofyc/go,goodlang/good,Cofyc/go,suncycheng/go,polyverse-security/go,polyverse-security/go,linux-on-ibm-z/go,akutz/go,vsekhar/elastic-go,momchil-velikov/go,cloudflare/go,golang/go,ImJasonH/go,ImJasonH/go,josharian/go,derekmarcotte/go,golang/go,suncycheng/go,golang/go,akutz/go,Cofyc/go,josharian/go,josharian/go,CAFxX/go,cloudflare/go,Cofyc/go,christopher-henderson/Go,ImJasonH/go,golang/go,momchil-velikov/go,suncycheng/go,codestation/go,codestation/go,akutz/go,momchil-velikov/go,Cofyc/go,cloudflare/go,akutz/go,nawawi/go,suncycheng/go,CAFxX/go,Cofyc/go,suncycheng/go,goodlang/good,vsekhar/elastic-go,cloudflare/go,derekmarcotte/go,golang/go,nawawi/go,josharian/go,derekmarcotte/go,goodlang/good,polyverse-security/go,ImJasonH/go,akutz/go,linux-on-ibm-z/go,polyverse-security/go,goodlang/good,akutz/go,nawawi/go,Cofyc/go,momchil-velikov/go,akutz/go,polyverse-security/go,derekmarcotte/go,linux-on-ibm-z/go,cloudflare/go,codestation/go,cloudflare/go,golang/go,derekmarcotte/go,momchil-velikov/go,golang/go,derekmarcotte/go,polyverse-security/go,suncycheng/go,derekmarcotte/go,CAFxX/go,vsekhar/elastic-go,ImJasonH/go,codestation/go,linux-on-ibm-z/go,vsekhar/elastic-go,linux-on-ibm-z/go,CAFxX/go,momchil-velikov/go,codestation/go,josharian/go