circleci: use Docker image v1.0.4

This new image which is already available contains Python3 support.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2.0
 jobs:
   build:
     docker:
-      - image: docker.io/openwrtorg/packages-cci:v1.0.3
+      - image: docker.io/openwrtorg/packages-cci:v1.0.4
     environment:
       - SDK_HOST: "downloads.openwrt.org"
       - SDK_PATH: "snapshots/targets/ath79/generic"