Puppet 6 adjustment

Since P6 has removed the `nagios_*` types from the core, we'll need to
put in an external dependency on them.

Since I'm not sure how breaking this change would be, I just bumped up
the Puppet dependency for sake of saving automation from itself.

metadata.json

@@ -21,13 +21,17 @@
   "requirements": [
     {
     "name": "puppet",
-    "version_requirement": ">=2.7.20 <6.0.0"
+    "version_requirement": ">=6.0.0 <7.0.0"
     }
   ],
   "dependencies": [
     {
     "name": "puppetlabs/stdlib",
     "version_requirement": ">= 3.2.0"
+    },
+    {
+      "name": "puppetlabs/nagios_core",
+      "version_requirement": ">= 1.0.2 < 2.0.0"
     }
   ]
 }