be more explicit with container registries in travis.
#!/usr/bin/env bash
-# Pull alpine base image from docker hub, but then retag it for $cr_server for reuse.
-docker pull "library/alpine:3.11" || true
-docker tag "library/alpine:3.11" "${cr_server}/wikipedialibrary/alpine:3.11"
+# Pull alpine base image from docker hub, but then retag it for $cr_server for reuse and mirroring.
+docker pull "docker.io/library/alpine:3.11" || true
+docker tag "docker.io/library/alpine:3.11" "${cr_server}/wikipedialibrary/alpine:3.11"
+
+# Build images with caching and then run the stack in docker-compose.
docker pull "${cr_server}/wikipedialibrary/twlight_base:${BRANCH_TAG}" || true
docker pull "${cr_server}/wikipedialibrary/twlight_build:${BRANCH_TAG}" || true
docker pull "${cr_server}/wikipedialibrary/twlight:${BRANCH_TAG}" || true
