Merge pull request #284 from puppetlabs/maint-add_puppet8

(maint) - Add puppet 8/Drop puppet 6

Author: LukasAud

metadata.json

@@ -46,7 +46,7 @@
   "requirements": [
     {
       "name": "puppet",
-      "version_requirement": ">= 4.6.1 < 7.0.0"
+      "version_requirement": ">= 7.0.0 < 9.0.0"
     }
   ],
   "pdk-version": "2.5.0",