byrnedo/alpine-curl for gitlab-ci

.gitlab-ci.yml

 packagist:
   image:
-    name: alpine:3.8
+    name: byrnedo/alpine-curl:0.1.6
     entrypoint: ['/bin/sh', '-c']
   script: |
-    apk add --no-cache curl
-    /usr/bin/curl "https://packagist.org/api/update-package?username=finc&apiToken=$PACKAGIST_API_TOKEN" \
+    : Publishing composer packages to packagist.org ...
+    /usr/bin/curl \
       --header 'content-type:application/json' \
-      --data '{"repository":{"url":"https://git.sc.uni-leipzig.de/ubl/finc/rules-evaluator"}}'
+      --data '{"repository":{"url":"https://git.sc.uni-leipzig.de/ubl/finc/rules-evaluator"}}' \
+      "https://packagist.org/api/update-package?username=finc&apiToken=$PACKAGIST_API_TOKEN"
   tags: [docker]
   only: [/^v/]
   except: [branches]
\ No newline at end of file