Fix root redirect for example.com/gitlab

The missing trailing / on example.com/gitlab was making us throw a
404.

upstream.go

@@ -107,7 +107,7 @@ func (u *upstream) ServeHTTP(ow http.ResponseWriter, r *http.Request) {
 
 	// Check URL Root
 	URIPath := cleanURIPath(r.URL.Path)
-	if !strings.HasPrefix(URIPath, u.relativeURLRoot) {
+	if !strings.HasPrefix(URIPath, u.relativeURLRoot) && URIPath+"/" != u.relativeURLRoot {
 		httpError(&w, r, fmt.Sprintf("Not found %q", URIPath), http.StatusNotFound)
 		return
 	}