add missing dependency

.gitlab-ci.yml

@@ -9,7 +9,7 @@ build-kernel:
       - "*.deb"
   script:
     - apt-get update
-    - apt-get install -y build-essential curl bison flex bc rsync kmod cpio lsb-release libssl-dev libelf-dev
+    - apt-get install -y build-essential curl bison flex bc rsync kmod cpio lsb-release libssl-dev libelf-dev zstd
     - ./compile.bash
   tags:
   - highmem