Set depth to 1 when fetch submodules

.drone.yml

@@ -7,7 +7,7 @@ steps:
 - name: Fetch Submodules
   image: alpine/git
   commands:
-  - git submodule update --recursive --remote
+  - git submodule update --recursive --depth=1 --remote
 
 - name: Testing
   image: ubuntu:bionic