GitlabAPI.getNotes(...) call creating non api v4 compliant URL

[Gulliteufel]

both methods to acces Notes from a GitlabIssue are ctearing an incorrect URL string.

The issue is identified by the ID but should be accessed with IID due to API V4 changes.

https://docs.gitlab.com/ce/api/notes.html

[PhilMFischer]

Can be closed due to pull request #284 .