CircleCI: update apt cache before installing packages.

 * apt cache on image not necessarily up-to-date, so need to update before
   doing any apt installs, see https://discuss.circleci.com/t/
   random-404-when-doing-apt-get-install-postgresql-client/30286

.circleci/config.yml

@@ -47,6 +47,7 @@ jobs:
            at: ~/.local
        - run:
            command: |
+             sudo apt update
              sudo apt install -y postgresql-client
              createdb -h localhost sndd -O root
              pip install --user psycopg2