Add `rbc` for `rebase --continue`

dotfiles/gittum/main.gitconfig

@@ -30,6 +30,7 @@
   ka = !sh -c \
        '(which gitk >/dev/null || (echo "gitk not installed" && false)) && gitk $@ --all' --
   rb = rebase
+  rbc = rebase --continue
   rbi = rebase --interactive
   rmv = remote --verbose
   sibling = ! ~/.gittum/bin/sibling