CI: make sure we log in for deployments (#1541)

Over at
#1514 (comment)
I suggested adding `deploy: false` to be less surprising with the
tags we're pushing to DockerHub.

As mentioned in #1512, we actually need `publish: true` to log in
with DockerHub.

.circleci/config.yml

@@ -124,7 +124,6 @@ workflows:
             - test
             - test_full
             - test_full_10
-          deploy: false
           image: sourcecred/sourcecred
           tag: latest
           cache_from: node:12,sourcecred/sourcecred:dev