Support organization PRs

[Turbo87]

Imagine that user foo opens a PR to lerna/lerna-changelog pointing to a branch in bar/lerna-changelog with bar being a GitHub organization. It might make sense to include the link to bar in the changelog next to the link to foo unless the org equals the org of the repo itself (bar === lerna in this case).

Example

• #60 Add support for homu merge commits. (@Turbo87 / @ember-cli)