chore: fix drone

.drone.yml

@@ -7,6 +7,7 @@ steps:
     image: plugins/docker
     settings:
       repo: ghcr.io/uetchy/uechi.io
+      cache_from: ghcr.io/uetchy/uechi.io:latest
       tags: latest
       registry: ghcr.io
       username:
@@ -18,7 +19,7 @@ steps:
     image: alpine/curl
     commands:
       - |
-        curl -s -H "Authorization: Bearer ${WATCHTOWER_TOKEN}" https://watchtower.uechi.dev/v1/update
+        curl -s -H "Authorization: Bearer $WATCHTOWER_TOKEN" https://watchtower.uechi.dev/v1/update
     environment:
       WATCHTOWER_TOKEN:
         from_secret: watchtower_token