Add volume for cargo registry

.drone.yml

@@ -4,6 +4,14 @@ name: default
 steps:
 - name: test
   image: rustlang/rust:nightly
+  volumes:
+  - name: cargo-registry
+    path: /usr/local/cargo/registry
   commands:
   - cargo build --verbose --all
   - cargo test --verbose --all
+
+volumes:
+- name: cache
+  host:
+    path: /var/lib/drone/sprinklers_rs/cargo-registry