BUGFIX: Set default gitlab-ci image (alpine) & switch commands

.gitlab-ci.yml

+image: 'bash:latest' 
+
 before_script:
   - apk add --no-cache make wget git
   - make install-composer
@@ -11,8 +13,7 @@ stages:
 sync:github:
   stage: sync
   before_script:
-    - apt-get -y update && apt-get -y upgrade
-    - apt-get -y install openssh-client git
+    - apk add --no-cache openssh-client git
     # SSH deploy key
     - eval $(ssh-agent -s)
     - ssh-add <(echo "$SSH_PRIVATE_KEY")