move shards install to install stage

.travis.yml

@@ -8,8 +8,8 @@ install:
   # Download hadolint binary and set it as executable
   - curl -sL -o ${HADOLINT} "https://github.com/hadolint/hadolint/releases/download/v1.17.5/hadolint-$(uname -s)-$(uname -m)"
     && chmod 700 ${HADOLINT}
-script:
   - shards install
+script:
   - crystal spec
   - crystal tool format --check
   - git ls-files --exclude='Dockerfile*' --ignored | xargs --max-lines=1 ${HADOLINT}