Set title for first heading

[arbox]

Change first heading from "bugs" to "issues". Not every Github issue is a bug.

[ardumont]

Hello,

Does this mean you propose this only for os-github.el?

./org-sync-redmine.el:159:         (title (concat "Bugs of " (org-sync-rmine-repo-name url))))
./org-sync-bb.el:186:         (title (concat "Bugs of " (org-sync-bb-repo-name url))))
./org-sync-github.el:103:         (title (concat "Bugs of " (org-sync-github-repo-name url))))

Cheers,