Update metadata.json.erb

This file should meet the defaults by the "Generate boilerplate for new modules".

https://github.com/puppetlabs/puppet/blob/master/lib/puppet/face/module/generate.rb

- The user should be able to define the version
- The description was replaced by the summary
- The issues_url is based on the project_page
- And puppetlabs-stdlib seems to be a default dependency