Fix proxy error codes

internal/proxy.go

@@ -70,14 +70,14 @@ func (s *Server) ProxyHandler() httprouter.Handle {
 		if err != nil {
 			msg := fmt.Sprintf("error making request to %s: %s", uri, err)
 			log.WithError(err).Error(msg)
-			http.Error(w, msg, http.StatusInsufficientStorage)
+			http.Error(w, msg, http.StatusBadGateway)
 			return
 		}
 
 		if n, err := io.Copy(w, res.Body()); err != nil {
 			msg := fmt.Sprintf("error copying proxied response (%d bytes copied)", n)
 			log.WithError(err).Error(msg)
-			http.Error(w, msg, http.StatusInsufficientStorage)
+			http.Error(w, msg, http.StatusInternalServerError)
 			return
 		}
 	}