Install bash in CI.

.gitlab-ci.yml

@@ -12,6 +12,7 @@ stages:
   - mirror
 
 before_script:
+  - apk add bash
   - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN $CI_REGISTRY
 
 mirror:

README.md

@@ -19,6 +19,7 @@ Ensure to add global `before_script`:
 
 ```
 before_script:
+  - apk add bash
   - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN $CI_REGISTRY
 ```