net/http: Incorrect comment for MethodPatch in method.go

[mqy]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?

go 1.6.2

1. What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOOS="darwin"

1. What did you do?

N/A

1. What did you expect to see?

incorrect comment for MethodPatch in net/http/method.go: "// RFC 5741" should be "// RFC 5789".
see rfc5789

1. What did you see instead?

N/A

[mikioh]

This is a duplicate of #15546.