godoc: fix initialization issue

R=rsc
CC=golang-dev
https://golang.org/cl/207111

src/cmd/godoc/godoc.go

@@ -100,7 +100,7 @@ var (
 )
 
 
-func initRoots() {
+func init() {
 	goroot = os.Getenv("GOROOT")
 	if goroot == "" {
 		goroot = pathutil.Join(os.Getenv("HOME"), "go")

src/cmd/godoc/main.go

@@ -152,7 +152,6 @@ func main() {
 		log.Exitf("negative tabwidth %d", *tabwidth)
 	}
 
-	initRoots()
 	readTemplates()
 
 	if *httpaddr != "" {