Infer repo URL from git metadata

[Turbo87]

When there is no package.json (or lerna.json) we should try to infer the repository URL from git remote metadata. This would be useful for non-JS projects that still want to use lerna-changelog.

Example

$ git remote get-url upstream
[email protected]:lerna/lerna-changelog.git

As apparently many people (including me) use upstream for the upstream repo and origin for their own fork, we should make sure to check the upstream remote before falling back to origin.