QmlJS: Fix completion of 'anchors.'.

The hasChildInPackage function was broken, so we completed 'anchors:'
instead.

Task-number: QTCREATORBUG-5180
Change-Id: I0e0d68aec3cf4e5bea991e39169beecf541ce477
Reviewed-on: http://codereview.qt.nokia.com/643


Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>