Switch Icinga/zf1 repo type from git to vcs (#105)

This change enables Composer to download dist archives (ZIP files) from GitHub
instead of cloning the full Git repository. Fixes 'warning: adding embedded git
repository' in GitHub Actions CI by avoiding .git dirs in vendor/.

Author: lippserd

composer.json

@@ -15,7 +15,7 @@
     },
     "repositories": [
       {
-        "type": "git",
+        "type": "vcs",
         "url": "https://github.com/Icinga/zf1"
       }
     ],