You can no longer add new DSA keys (ssh-dss) to your GitHub account. Existing DSA keys are not affected and will continue to function. All GitHub Enterprise versions of 2.18 and prior will allow DSA keys to be added.
GitHub Enterprise 2.19 will no longer provide this functionality.
When an issue is referenced with a closing keyword in a pull request description, the referenced issue will now surface the relevant pull request information in its header (eg: fixed by #15).
Learn more about closing issues using keywords on GitHub
