fix .drone.yml

.drone.yml

@@ -29,7 +29,7 @@ steps:
       - apt-get update
       - apt-get install -y --no-install-recommends build-essential ca-certificates curl git ssh libssl-dev
       - curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain stable --no-modify-path
-      - source $HOME/.cargo/env
+      - . $HOME/.cargo/env
       - npm install
       - npm run export
       - cp __sapper__/build/server/assets/*.wasm __sapper__/export/assets/