Fix module data provider

This commit sets the data provider to Hiera.  A previous update added
the `hiera.yaml` file and `/data` directories, but they have not
actually been used.  It went unnoticed, because they were empty.  Fixing
this allows future changes to use the module data system.

metadata.json

@@ -7,6 +7,7 @@
   "source": "https://github.com/voxpupuli/puppet-yum.git",
   "project_page": "https://github.com/voxpupuli/puppet-yum",
   "issues_url": "https://github.com/voxpupuli/puppet-yum/issues",
+  "data_provider": "hiera",
   "dependencies": [
     {
       "name": "puppetlabs/stdlib",