add step to fetch with lfs

.drone.yml

@@ -13,6 +13,11 @@ steps:
   settings:
     recursive: true
 
+- name: fetch images
+  images: alpine/git
+  commands:
+    - git lfs fetch
+
 - name: pandoc
   image: pandoc/core:2.18-alpine
   commands:
@@ -55,6 +60,6 @@ steps:
     prerelease: true
 ---
 kind: signature
-hmac: d2d18baa658a4f39063bf6190626363bcf6d3b7815c60400a15b95d18b1feb43
+hmac: 2a8d8c7147dee472ce79f7564db1ae208a8e131b7659f0e15c9f90a7c05f9011
 
 ...