net/http: correct RFC for MethodPatch

Fixes #15546.

Change-Id: I39c29ea6999812dd5f1c45f67bddad28f20b6c6b
Reviewed-on: https://go-review.googlesource.com/22773Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/method.go

@@ -12,7 +12,7 @@ const (
 	MethodHead    = "HEAD"
 	MethodPost    = "POST"
 	MethodPut     = "PUT"
-	MethodPatch   = "PATCH" // RFC 5741
+	MethodPatch   = "PATCH" // RFC 5789
 	MethodDelete  = "DELETE"
 	MethodConnect = "CONNECT"
 	MethodOptions = "OPTIONS"