Metadata attributes being dropped

[nathenharvey]

When publishing a cookbook with metadata.rb that includes source_url and issues_url, the attributes are not sent to the Supermarket.

As a result, the "View Source" and "View Issues" links cannot be managed through the metadata of the cookbook.

[nathenharvey]

@sethvargo is it as easy as adding those two attributes to the hash definition? https://github.com/sethvargo/stove/blob/master/lib/stove/cookbook/metadata.rb#L159-179

[sethvargo]

Yea - those just didn't exist when I wrote stove. Do you want to open a PR? If not, I can fix it later

[nathenharvey]

PR 71