Bump required puppet version 4.6.1->4.7.0

4.6.1 was recommended while we did our upgrade from puppet3 to puppet4.
However: There were some bugs in 4.6 and puppetlabs made 4.7.0 the new
recommended and LTS version.

metadata.json

@@ -79,7 +79,7 @@
   "requirements": [
     {
       "name": "puppet",
-      "version_requirement": ">= 4.6.1 < 5.0.0"
+      "version_requirement": ">= 4.7.0 < 5.0.0"
     }
   ],
   "name": "puppet-collectd",