Drop puppet4; require at least Puppet 5.5.8

Author: bastelfreak

metadata.json

@@ -50,7 +50,7 @@
   "requirements": [
     {
       "name": "puppet",
-      "version_requirement": ">= 4.10.0 < 7.0.0"
+      "version_requirement": ">= 5.5.8 < 7.0.0"
     }
   ]
 }