content/static: add gopath_code.html file and regenerate

CL 199417 added a new doc/gopath_code.html file. This change adds
it to the list of files that are embedded in package static, and
regenerates the package.

A change described in https://golang.org/issue/29206#issuecomment-536099768
will make it no longer neccessary to do this step in the future.

Updates golang/go#28215
Updates golang/go#29206

Change-Id: Ia1bd125488e04b34f9b8e36de4397de32d77bcef
Reviewed-on: https://go-review.googlesource.com/c/website/+/213937
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>

Author: dmitshur

content/static/gen.go

@@ -41,6 +41,7 @@ var files = []string{
 	"doc/devel/release.html",
 	"doc/devel/weekly.html",
 	"doc/docs.html",
+	"doc/gopath_code.html",
 	"doc/root.html",
 	"doc/security.html",
 	"error.html",