* contrib/lisp/ox-taskjuggler.el (org-taskjuggler-target-version): The
default target is now tj3
Since taskjuggler is not developed anymore and hardly any
distributions carry it anymore we ought to target tj3 by default now.
* contrib/lisp/ox-taskjuggler.el (org-taskjuggler--build-task): Fix
the check whether a node has no children
A milestone should only (automatically) be inserted if a node has no
children and no duration defined.