Fix typo in header name

Author: Hexawolf

server.go

@@ -349,7 +349,7 @@ func (s *Server) serveFile(w http.ResponseWriter, r *http.Request) {
 // Note that filedrop code is URL prefix-agnostic, so request URI doesn't
 // matters much.
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("Access-Control-Allowed-Origin", s.Conf.AllowedOrigins)
+	w.Header().Set("Access-Control-Allow-Origin", s.Conf.AllowedOrigins)
 	if r.Method == http.MethodPost {
 		s.acceptFile(w, r)
 	} else if