gddo-server: change redirects to 301

Change-Id: Ie2c31f719a29d3cd2eb7b449bf9908fae875b168
Reviewed-on: https://go-review.googlesource.com/c/gddo/+/289730
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Trust: Julie Qiu <julie@golang.org>

gddo-server/pkgsite.go

diff --git a/gddo-server/pkgsite.go b/gddo-server/pkgsite.go
index 52c477d..c623db8 100644
--- a/gddo-server/pkgsite.go
+++ b/gddo-server/pkgsite.go
@@ -199,7 +199,7 @@
 		redirectURL := pkgGoDevURL(r.URL).String()
 		if configPoller != nil {
 			if shouldRedirectURL(r, configPoller) {
-				http.Redirect(w, r, redirectURL, http.StatusFound)
+				http.Redirect(w, r, redirectURL, http.StatusMovedPermanently)
 				return nil
 			}
 		}