feat(ci): add missing dependencies

.drone.yml

@@ -16,6 +16,8 @@ steps:
       PGHOST: &db_host db
     commands:
       - while ! pg_isready; do sleep 1; done
+    depends_on:
+      - 'db'
 
   - name: restore cache
     image: &drone_cache 'meltwater/drone-cache:v1.4.0'
@@ -49,6 +51,8 @@ steps:
       - mix do local.rebar --force, local.hex --force, deps.get, deps.compile
       - mix compile --force --all-warnings --warnings-as-errors
     volumes: *volumes
+    depends_on:
+      - 'restore cache'
 
   - name: test
     image: *elixir