build musl images

.drone.yml

@@ -3,11 +3,11 @@ name: default
 
 steps:
  - name: test
-   image: rust:1.38.0
+   image: rust:1.38.0-alpine
    commands:
     - cargo test
  - name: build_relase
-   image: rust:1.38.0
+   image: rust:1.38.0-alpine
    commands:
     - cargo install --path . --root . -f
     - strip bin/tictactoe