First shot at cache

.drone.yml

@@ -7,6 +7,15 @@ platform:
   arch: arm64
 
 steps:
+  - name: restore cache
+    image: meltwater/drone-cache:dev
+    settings:
+      backend: "sftp"
+      restore: true
+      archive_format: "gzip"
+      mount:
+        - 'vendor'
+
   - name: unit tests
     image: rust:1.49.0-slim
     commands:
@@ -41,3 +50,12 @@ steps:
       - chmod u=rw,go= /tmp/rsync_key
       - rsync -e 'ssh -i /tmp/rsync_key -o "UserKnownHostsFile ../.ci/known_hosts"' -vaz --delete ./book/ space_docs_librepush_net@sallie.librepush.net:./public/yama
       - rm /tmp/rsync_key
+
+  - name: rebuild cache
+    image: meltwater/drone-cache:dev
+    settings:
+      backend: "sftp"
+      rebuild: true
+      archive_format: "gzip"
+      mount:
+        - 'vendor'