Closed issues in source repo should be imported as closed

The problem I'm trying to solve is that an issue `closed` in the source repository it will be imported as `open` in the target repository. The problem was discussed already in this issue: https://github.com/IQAndreas/github-issues-import/issues/14.

The solution is that an additional PATCH request is made to `close` the issue after it's created in the target repository.