Improve node modification when using attributes to identify the target node

[Mauro]

When trying to modify a node using attributes to identify the target node, currently it is not possible to do something like:

@source.document.html.body.div({ 'class' => 'cucumber' }).script({ 'id' => 'script_totals' }) = totals

[Mauro]

Workaround:

@source.document.html.body.div({ 'class' => 'cucumber' }).send(:script=, { 'id' => 'script_totals' }, totals)